How to find eulerian circuit

A graph G is called an Eulerian Graph if there exists a closed traversable trail, called an Eulerian trail. A finite connected graph is Eulerian if and only if each vertex has even degree. Euler proved that a necessary condition for the existence of Eulerian circuits is that all vertices in the graph have an even degree.

How to find eulerian circuit. Euler Paths and Euler Circuits Finding an Euler Circuit: There are two different ways to find an Euler circuit. 1. Fleury’s Algorithm: Erasing edges in a graph with no odd vertices and keeping track of your progress to find an Euler Circuit. a. Begin at any vertex, since they are all even. A graph may have more than 1 circuit). b.

Euler's solution for Konigsberg Bridge Problem is considered as the first theorem of Graph Theory which gives the idea of Eulerian circuit. It can be used in several cases for shortening any path.

As there is only one vertex in this graph, and depending on what the graph looks like (a single vertex without an edge or a single vertex with a loop), we find that every top has even degree. It is also trivial to notice that this is a connected graph, so we deduce, by a theorem proven by Euler, that this graph contains an eulerian cyclus.May 11, 2018 · I've got this code in Python. The user writes graph's adjency list and gets the information if the graph has an euler circuit, euler path or isn't eulerian. Since we're after a path, essentially you want to find any path between the two vertices of odd degree, removing the edges you traverse along the way. Next, pick a vertex along this path that still has edges incident to it. Find any circuit from that vertex back to itself, again removing any edges traversed.The Euler Circuit is a special type of Euler path. When the starting vertex of the Euler path is also connected with the ending vertex of that path, then it is called the Euler Circuit. To check whether a graph is Eulerian or not, we have to check two conditions −. The graph must be connected. The in-degree and out-degree of each vertex must ...Aug 8, 2020 · 1. If a directed graph D = (V, E) D = ( V, E) has a DFS tree that is spanning, and has in-degree equal out-degree, then it is Eulerian (ie, has an euler circuit). So this algorithm works fine. Proof. Assume it does not have an Eulerian circuit, and let C C be a maximal circuit containing the root, r r, of the tree (such circuits must exist ... Here 1->2->4->3->6->8->3->1 is a circuit. Circuit is a closed trail. These can have repeated vertices only. 4. Path – It is a trail in which neither vertices nor edges are repeated i.e. if we traverse a graph such that we do not repeat a vertex and nor we repeat an edge. As path is also a trail, thus it is also an open walk.

Push the vertex that we stuck to the top of the stack data structure which holds the Eulerian Cycle. Backtrack from this vertex to the previous one. If there are edges to follow, we have to return ...May 8, 2014 · In the general case, the number of distinct Eulerian paths is exponential in the number of vertices n. Just counting the number of Eulerian circuits in an undirected graph is proven to be #P-complete (see Note on Counting Eulerian Circuits by Graham R. Brightwell and Peter Winkler). Learning Outcomes. Add edges to a graph to create an Euler circuit if one doesn’t exist. Find the optimal Hamiltonian circuit for a graph using the brute force algorithm, the nearest neighbor algorithm, and the sorted edges algorithm. Use Kruskal’s algorithm to form a spanning tree, and a minimum cost spanning tree.In the previous section, we found Euler circuits using an algorithm that involved joining circuits together into one large circuit. You can also use Fleury's algorithm to find Euler circuits in any graph with vertices of all even degree. In that case, you can start at any vertex that you would like to use. Step 1: Begin at any vertex.So it is easy to find a cycle in G G: pick any vertex g g and go from vertex to vertex until you finish again at g g; you cannot get stuck. Having found this cycle C C, there are either no unmarked edges, in which case C C is itself an Eulerian cycle of G G, or else there is some vertex v v of C C which is incident to an unmarked edge. (If ...Printing Eulerian Path using Fleury's Algorithm. We need to take a look at specific standards to get the way or circuit −. ️Ensure the chart has either 0 or 2 odd vertices. ️Assuming there are 0 odd vertices, begin anyplace. Considering there are two odd vertices, start at one of them. ️Follow edges each in turn.

Textbook solution for Mathematics All Around (6th Edition) 6th Edition Tom Pirnot Chapter 4.1 Problem 14E. We have step-by-step solutions for your textbooks written by Bartleby experts!This graph does have Euler circuits. Figure 1-15(c) in text. Page 5. An Euler Path.Section 4.4 Euler Paths and Circuits ¶ Investigate! 35. An Euler path, in a graph or multigraph, is a walk through the graph which uses every edge exactly once. An Euler circuit is an Euler path which starts and stops at the same vertex. Our goal is to find a quick way to check whether a graph (or multigraph) has an Euler path or circuit.A Computer Science portal on geeks. It contains well writing, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions.

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Eulerian circuits and graphs. Returns True if and only if G is Eulerian. Returns an iterator over the edges of an Eulerian circuit in G. Transforms a graph into an Eulerian graph. Return True iff G is semi-Eulerian. Return True iff G …Eulerian Circuit; Node Junction; These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves. Download chapter PDF Author information. Authors and Affiliations. Humboldt-Universität zu Berlin, Berlin, Germany ...An Euler tour or Eulerian tour in an undirected graph is a tour/ path that traverses each edge of the graph exactly once. Graphs that have an Euler tour are called Eulerian graphs. Necessary and sufficient conditions. An undirected graph has a closed Euler tour if and only if it is connected and each vertex has an even degree.Use Fleury’s algorithm to find an Euler circuit; Add edges to a graph to create an Euler circuit if one doesn’t exist; Identify whether a graph has a Hamiltonian circuit or path; Find the optimal Hamiltonian circuit for a graph using the brute force algorithm, the nearest neighbor algorithm, and the sorted edges algorithmMany different methods can be used to approximate the solution of differential equations. So, understand the Euler formula, which is used by Euler's method calculator, and this is one of the easiest and best ways to differentiate the equations. Curiously, this method and formula originally invented by Eulerian are called the Euler method.

To know if a graph is Eulerian, or in other words, to know if a graph has an Eulerian cycle, we must understand that the vertices of the graph must be positioned where each edge is visited once and that the …After such analysis of euler path, we shall move to construction of euler trails and circuits. Construction of euler circuits Fleury's Algorithm (for undirected graphs specificaly) This algorithm is used to find the euler circuit/path in a graph. check that the graph has either 0 or 2 odd degree vertices. If there are 0 odd vertices, start ...2 Answers. Bipartite ... Only Red and Blue vertices are joined. An even number of vertices ... 3 + 5 = 8 3 + 5 = 8. Eulerian ... each vertex has even valency. But ... there is clearly no matching. Hint: In a bipartite graph, any edge in a matching must go from one half to the other. Using only this fact, can you think of a very simple criterion ...TAATGCCATGGGATGTT, has nine maximal non-branching paths that spell out the contigs TAAT, TGTT, TGCCAT, ATG, ATG, ATG, TGG, GGG, and GGAT → because of repeats, it becomes harder to infer a unique Eulerian path without using read pairs as they only work with perfect coverage and it's often rare to get said read-pairs.An Eulerian circuit is an Eulerian path that starts and ends at the same vertex. In the above example, we can see that our graph does have an Eulerian circuit. If your graph does not contain an Eulerian cycle then you may not be able to return to the start node or you will not be able to visit all edges of the graph.6 Answers. 136. Best answer. A connected Graph has Euler Circuit all of its vertices have even degree. A connected Graph has Euler Path exactly 2 of its vertices have odd degree. A. k -regular graph where k is even number. a k -regular graph need not be connected always.HIERHOLZER'S ALGORITHM. It is an algorithm to find the Euler Path or Euler circuit in a graph. Even in Fleury's algorithm we can also print the Euler Path in a graph but its time complexity is O(E 2).In Hierholzer's algorithm can find Euler Path in linear time, O(E).. Hierholzer's algorithm-without stack. Any starting vertex v is chosen, a trail of edges from that vertex until the end ...So it is easy to find a cycle in G G: pick any vertex g g and go from vertex to vertex until you finish again at g g; you cannot get stuck. Having found this cycle C C, there are either no unmarked edges, in which case C C is itself an Eulerian cycle of G G, or else there is some vertex v v of C C which is incident to an unmarked edge. (If ...Fleury's algorithm, named after Paul-Victor Fleury, a French engineer and mathematician, is a powerful tool for identifying Eulerian circuits and paths within graphs. Fleury's algorithm is a precise and reliable method for determining whether a given graph contains Eulerian paths, circuits, or none at all. By following a series of steps ...Polygons and Vertices. For Students 9th - 12th. In this geometry worksheet, students analyze different polygons and relate it to a circuit board. They find the odd degree Euler circuit and identify the vertices of the odd degree. There are 3 questions with an answer key. +.

The most salient difference in distinguishing an Euler path vs. a circuit is that a path ends at a different vertex than it started at, while a circuit stops where it starts. An Eulerian graph is ...

Two bridges must be built for an Euler circuit. 9. Below is a graph representing friendships between a group of students (each vertex is a student and each edge is a friendship). Is it possible for the students to sit around a round table in such a way that every student sits between two friends? What does this question have to do with paths?3 Answers. Sorted by: 5. If a Eulerian circut exists, then you can start in any node and color any edge leaving it, then move to the node on the other side of the edge. Upon arriving at a new node, color any other edge leaving the new node, and move along it. Repeat the process until you.I don't see its definition in your listing. Please see "minimal compilable example" However, you have defined a method that takes a reference to a node and an array of bools: void node::DFSUtil(node &a,bool visited[]) I imagine the compiler is complaining that your call with those params doesn't match any method or function that it …Approach. We will be using Hierholzer's algorithm for searching the Eulerian path. This algorithm finds an Eulerian circuit in a connected graph with every vertex having an even degree. Select any vertex v and place it on a stack. At first, all edges are unmarked. While the stack is not empty, examine the top vertex, u.It may look like one big switch with a bunch of smaller switches, but the circuit breaker panel in your home is a little more complicated than that. Read on to learn about the important role circuit breakers play in keeping you safe and how...In this video I will tell you how to use the Hierholzer's Algorithm to find the Eulerian Path/Circuit.Have a wonderful Valentines Day! 💕Please like, subscri...A graph G is called an Eulerian Graph if there exists a closed traversable trail, called an Eulerian trail. A finite connected graph is Eulerian if and only if each vertex has even degree. Euler proved that a necessary condition for the existence of Eulerian circuits is that all vertices in the graph have an even degree.An Eulerian graph is a graph that possesses an Eulerian circuit. Example 9.4.1 9.4. 1: An Eulerian Graph. Without tracing any paths, we can be sure that the graph below has an Eulerian circuit because all vertices have an even degree. This follows from the following theorem. Figure 9.4.3 9.4. 3: An Eulerian graph.

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An Eulerian Trail is a trail that uses every edge of a graph exactly once and starts and ends at different vertices. A Eulerian Circuit is a circuit that uses every edge of a network exactly one and starts and ends at the same vertex.The following videos explain Eulerian Trails and Circuits in the QCE General Maths course. The following video explains this …1. One way of finding an Euler path: if you have two vertices of odd degree, join them, and then delete the extra edge at the end. That way you have all vertices of even degree, and your path will be a circuit. If your path doesn't include all the edges, take an unused edge from a used vertex and continue adding unused edges until you get a ...In graph theory, an Eulerian trail is a trail in a finite graph that visits every edge exactly once . Similarly, an Eulerian circuit or Eulerian cycle is an Eulerian trail that starts and ends on the same vertex. They were first discussed by Leonhard Euler while solving the famous Seven Bridges of Königsberg problem in 1736. The problem can be stated …vertex has even degree, then there is an Euler circuit in the graph. Buried in that proof is a description of an algorithm for nding such a circuit. (a) First, pick a vertex to the the \start vertex." (b) Find at random a cycle that begins and ends at the start vertex. Mark all edges on this cycle. This is now your \curent circuit."Anyone who enjoys crafting will have no trouble putting a Cricut machine to good use. Instead of cutting intricate shapes out with scissors, your Cricut will make short work of these tedious tasks.Hence the graph is Eulerian and the answer is True. For the second test case, 'edged' = [ [0, 1]], describing the following graph: Here you can see the path [0 -> 1] uses all the edges but does not start and end at the same location. Hence there is no Euler circuit in the graph and the answer is False.1, then we call it a closed trail or a circuit (in this case, note that ' 3). A trail (resp., circuit) that uses all the edges of the graph is called an Eulerian trail (resp., Eulerian circuit). If a trail v 1v 2:::v '+1 satis es that v i 6= v j for any i 6= j, then it is called a path. A subgraph of G is a graph (V 0;E 0) such that V V and ...I know I can see if an Eulerian cycle exists counting the number of vertexes in the graph having odd and even edges joining other vertexes. If all vertexes have an even number, or exactly two uneven, of connected lines, …Finding Euler Circuits Given a connected, undirected graph G = (V,E), find an Euler circuit in G. even. Using a similar algorithm, you can find a path Euler Circuit Existence Algorithm: Check to see that all vertices have even degree Running time = Euler Circuit Algorithm: 1. Do an edge walk from a start vertex until youDec 2, 2015 · At that point you know than an Eulerian circuit must exist. To find one, you can use Fleury's algorithm (there are many examples on the web, for instance here). The time complexity of the Fleury's algorithm is O(|E|) where E denotes the set of edges. But you also need to detect bridges when running the algorithm. 1 Answer. Consider the following: If you have m + n m + n vertices and the bipartite graph is complete, then you can send an edge from each of the m m vertices on one side to each of the n n vertices on the other side. Since for each m m you have n n possibilities, then e(Km,n) = mn e ( K m, n) = m n . Now the degree of each vertex on the V0 V ... ….

An example of using the first construction. Clearly the first image contains an Eulerian Circuit that begins and ends at A. By adding the green edge, an Eulerian walk can be found that follows the circuit from the first image, then simply follows the edge connecting \(A\) and \(D\). Alternatively, such a construction can be made by starting with a graph E where all of the vertices are of even ...At this point We need to prove that the answer contains every edge exactly once (that is, the answer is Eulerian), and this follows from the fact that every edge is explored at most once, since it gets removed from the graph whenever it is picked, and from the fact that the algorithm works as a DFS, therefore it explores all edges and each time ...I would like to generate a Eulerian circuit of this graph (visit each edge exactly once). One solution is to run the DFS-based algorithm that can find a Eulerian circuit in any Eulerian graph (a graph with all vertices of even degree).Problem 3. (20 pts) For each of the three graphs in Figure 1, determine whether they have an Euler walk and/or an Euler circuit. Justify your answer, i.e. if an Euler walk or circuit exists, construct it explicitly, and if not give a proof of its non-existence. Solution. The vertices of K 5 all have even degree so an Eulerian circuit exists, namelyThe Euler Circuit is a special type of Euler path. When the starting vertex of the Euler path is also connected with the ending vertex of that path, then it is called the Euler Circuit. To detect the path and circuit, we have to follow these conditions −. The graph must be connected. When exactly two vertices have odd degree, it is a Euler Path.0. The graph for the 8 x 9 grid depicted in the photo is Eulerian and solved with a braiding algorithm which for an N x M grid only works if N and M are relatively prime. A general algorithm like Hierholzer could be used but its regularity implies the existence of a deterministic algorithm to traverse the (2N+1) x (2M +1) verticies of the graph.with the Eulerian trail being e 1 e 2... e 11, and the odd-degree vertices being v 1 and v 3. Am I missing something here? "Eulerian" in the context of the theorem means "having an Euler circuit", not "having an Euler trail". Ahh I actually see the difference now.def eulerian_circuit(graph): """ Given an Eulerian graph, find one eulerian circuit. Returns the circuit as a list of nodes, with the first and last node being the same.Pick up a starting Vertex. Condition 1: If all Nodes have even degree, there should be a euler Circuit/Cycle. We can pick up any vertex as starting vertex. Condition 2: If exactly 2 nodes have odd degree, there should be euler path. We need to pick up any one of this two as starting vertex. Condition 3: If more than 2 nodes or exactly one node ... How to find eulerian circuit, Create a cycle e.g. 3->6->5->2->0->1->4->3 because Euler cycle should be connected graph. Then creating random edges. Saving graph to file. Finding Euler cycle is based od DFS. Finding Euler cycle works for 100,200,300 nodes. When it's e.g. 500, application don't show Euler cycle. If you have any suggestions, what should I change in code, post ..., Now, if we increase the size of the graph by 10 times, it takes 100 times as long to find an Eulerian cycle: >>> from timeit import timeit >>> timeit (lambda:eulerian_cycle_1 (10**3), number=1) 0.08308156998828053 >>> timeit (lambda:eulerian_cycle_1 (10**4), number=1) 8.778133336978499. To make the runtime linear in the number of edges, we have ..., Now, if we increase the size of the graph by 10 times, it takes 100 times as long to find an Eulerian cycle: >>> from timeit import timeit >>> timeit (lambda:eulerian_cycle_1 (10**3), number=1) 0.08308156998828053 >>> timeit (lambda:eulerian_cycle_1 (10**4), number=1) 8.778133336978499. To make the runtime …, Q: Find any • Euler paths, • Euler circuits, • Hamilton paths, and/or • Hamilton circuits if possible… A: Euler path touches every edge only one time and ends in a different vertice other than the starting…, I managed to create an algorithm that finds an eulerian path(if there is one) in an undirected connected graph with time complexity O(k^2 * n) where: k: number of edges . n: number of nodes . I would like to know if there is a better algorithm, and if yes the idea behind it. Thanks in advance!, 2 Answers. A graph is eulerian iff it has a Eulerian circuit. If you remove an edge, what was once a Eulerian circuit becomes a Eulerian path, so if the graph was connected, it stays connected. An eulerian Graph has a eulerian circuit (for example by Hierholzers algorithm) that visits each vertex twice and doesn't use the same edge twice., In this video, we will see #Euler's method using MATLAB to find the solution of a differential equation of the basic circuit like the RC circuit. #Eulers met..., May 11, 2021 at 11:22. 10c2 is the permutation. - Aragorn. May 11, 2021 at 11:26. Add a comment. 4. Indeed, for Eulerian graphs there is a simple characterization, whereas for Hamiltonian graphs one can easily show that a graph is Hamiltonian (by drawing the cycle) but there is no uniform technique to demonstrate the contrary., 1. If a directed graph D = (V, E) D = ( V, E) has a DFS tree that is spanning, and has in-degree equal out-degree, then it is Eulerian (ie, has an euler circuit). So this algorithm works fine. Proof. Assume it does not have an Eulerian circuit, and let C C be a maximal circuit containing the root, r r, of the tree (such circuits must exist ..., A circuit is any path in the graph which begins and ends at the same vertex. Two special types of circuits are Eulerian circuits, named after Leonard Euler (1707 to 1783), and Hamiltonian circuits named after William Rowan Hamilton (1805 to 1865). The whole subject of graph theory started with Euler and the famous Konisberg Bridge Problem., While it usually is possible to find an Euler circuit just by pulling out your pencil and trying to find one, the more formal method is Fleury's algorithm. Fleury's Algorithm. 1. Start at any vertex if finding an Euler circuit. If finding an Euler path, start at one of the two vertices with odd degree. 2. Choose any edge leaving your ..., proved it last week) and it is Eulerian. Otherwise, let G' be the graph obtained by deleting a cycle. The lemma we just proved shows it is always possible to delete a cycle. By induction hypothesis, G' is Eulerian. To build a Eulerian circuit in G, start by the cycle we just deleted, and append the Eulerian circuit of G'., May 11, 2021 at 11:22. 10c2 is the permutation. - Aragorn. May 11, 2021 at 11:26. Add a comment. 4. Indeed, for Eulerian graphs there is a simple characterization, whereas for Hamiltonian graphs one can easily show that a graph is Hamiltonian (by drawing the cycle) but there is no uniform technique to demonstrate the contrary., A brief explanation of Euler and Hamiltonian Paths and Circuits.This assumes the viewer has some basic background in graph theory. The Seven Bridges of König..., For me, the most useful one was Wikipedia. But as far as I understood, in order to use this algorithm, you have to check, if there is Eulerian path (using properties: for undirected graph — the graph should be connected (and probably has vertices without edges) and <= 2 vertices should have odd degree. for directed graph — the graph should be strongly …, When the circuit ends, it stops at a, contributes 1 more to a's degree. Hence, every vertex will have even degree. We show the result for the Euler path next before discussing the su cient condition for Euler circuit. First, suppose that a connected multigraph does have an Euler path from a to b, but not an Euler circuit., The process to Find the Path: First, take an empty stack and an empty path. If all the vertices have an even number of edges then start from any of them. If two of the vertices have an odd number of edges …, A specific circuit-remover matrix O =11T−I O = 1 1 T − I, Where 1 1 is the column vector of N N ones. ( O O is basically a logically inverted unit matrix, 0 0 on diagonal and 1 1 everywhere else) Now define the matrix : {T0 =MTk+1 =M(O ⊗ Tk) { T 0 = M T k + 1 = M ( O ⊗ T k) Then calculate the sum., This problem has been solved! You'll get a detailed solution from a subject matter expert that helps you learn core concepts. See Answer. Question: (2) For the graph below a) Find an Eulerian circuit, or prove that none exists. (b) Find a Hamiltonian circuit or prove that none exists. Show transcribed image text., Use Fleury's algorithm to find an Euler circuit; Add edges to a graph to create an Euler circuit if one doesn't exist; Identify whether a graph has a Hamiltonian circuit or path; Find the optimal Hamiltonian circuit for a graph using the brute force algorithm, the nearest neighbor algorithm, and the sorted edges algorithm ..., A circuit is a trail that begins and ends at the same vertex. The complete graph on 3 vertices has a circuit of length 3. The complete graph on 4 vertices has a circuit of length 4. the complete graph on 5 vertices has a circuit of length 10. How can I find the maximum circuit length for the complete graph on n vertices? , Now, find a different Euler circuit that starts at vertex A, on your own. Example 1: By trial and error, find an Euler path for Figure A and an Euler circuit for Figure B. Figure A Figure B. Example 3: Consider the graph presented below: a) Use Euler͛s Theorem to explain why gr aph below has at least one Euler path. Solution:, Accepted Answer. You can try utilising the Matgraph toolbox for your problem. A function euler_trail exists in the toolbox which may help you in proceeding with your task. Below is the link to the toolbox: Please go through the above link and add the Matgraph add-on in Matlab. For undirected graphs in Matlab, please refer to the below ..., This is an algorithm to find an Eulerian circuit in a connected graph in which every vertex has even degree. 1. Choose any vertex v and push it onto a stack. Initially all edges are unmarked. 2. While the stack is nonempty, look at the top vertex, u, on the stack. If u has an unmarked incident edge, say, to a vertex w, then push w onto the ..., Euler paths and circuits : An Euler path is a path that uses every edge of a graph exactly once. An Euler circuit is a circuit that uses every edge of a graph exactly once. An Euler path starts and ends at different vertices. An Euler circuit starts and ends at the same vertex. The Konigsberg bridge problem's graphical representation :, An Euler circuit is a circuit that uses every edge of a graph exactly once. An Euler path starts and ends at different vertices. An Euler circuit starts and ends at the same vertex. The Konigsberg bridge problem’s graphical representation : There are simple criteria for determining whether a multigraph has a Euler path or a Euler circuit., Modified 2 years, 1 month ago. Viewed 6k times. 1. From the way I understand it: (1) a trail is Eulerian if it contains every edge exactly once. (2) a graph has a closed Eulerian trail iff it is connected and every vertex has even degree. (3) a complete bipartite graph has two sets of vertices in which the vertices in each set never form an ..., * To compute Eulerian cycles and paths in digraphs, see * {@link DirectedEulerianCycle} and {@link DirectedEulerianPath} ..., Subject classifications. An Eulerian path, also called an Euler chain, Euler trail, Euler walk, or "Eulerian" version of any of these variants, is a walk on the graph edges of a graph which uses each graph edge in the original graph exactly once. A connected graph has an Eulerian path iff it has at most two graph vertices of odd degree., I would like to generate a Eulerian circuit of this graph (visit each edge exactly once). One solution is to run the DFS-based algorithm that can find a Eulerian circuit in any Eulerian graph (a graph with all vertices of even degree)., If we have a Graph with Euler Circuit can we the consider it as a special Euler Path that start and end in the same Node? I am asking because the Condition of Euler Path is that we have 0 or 2 Nodes with an odd degree so but the graph with 0 nodes with odd degrees will have an Euler Circuit. graph-theory;, May 11, 2018 · I've got this code in Python. The user writes graph's adjency list and gets the information if the graph has an euler circuit, euler path or isn't eulerian. , Note that circuits and Eulerian subgraphs are the same thing. This means that finding the longest circuit in G is equivalent to finding a maximum Eulerian subgraph of G. As noted above, this problem is NP-hard. So, unless P=NP, an efficient (i.e. polynomial time) algorithm for finding a maximal Eulerian subgraph in an arbitrary graph is impossible.