An Eulerian Cycle (or Eulerian Circuit) is a path in a graph that visits every edge exactly once and returns to the starting node. In an undirected graph, an Eulerian cycle exists if and only if every vertex has an even degree and all vertices with non-zero degree belong to a single connected component. It is closely related to the famous Seven Bridges of Königsberg problem.
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An Eulerian Path visits every edge in a graph exactly once and exists if exactly 0 or 2 vertices have an odd degree. An Eulerian Cycle is an Eulerian Path that starts and ends at the same vertex, which requires every vertex to have an even degree (0 odd degree vertices).
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