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| − | <pre>
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| − | Working with the list of edges of an undirected graph G
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| − | Read the edges of G and create an adjacency matrix A, and simultaneously calculate the degree of each vertex in the array B # O(m)
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| − | - Consider an edge UW, if the data about it already exists A[U][W] == A[W][U] == 1, then a multiple edge is found, skip it
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| − | Initialize the queue Q
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| − | Add to Q all vertexes whose degree is 2 # O(n) iterations, O(1) get the vertex degree via the array B
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| − | - The presence of a vertex in the queue is noted in the array C, which consists of bool flags
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| − | Loop until the queue Q is empty: # O(n) iterations
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| − | - Extract vertex V from Q # V has degree 2 => V located between vertexes U and W
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| − | - Delete the edge UV, B[U] -= 1
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| − | - Delete the edge VW, B[W] -= 1
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| − | - Delete vertex V, C[V] = False
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| − | - If U and W are not adjacent, connect U and W with an edge and increase the degrees of U and W by 1 # Checking the adjacency O(1) via the adjacency matrix
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| − | - If U's degree is 2 and U is not in queue Q, add U to Q # Getting vertex degree via B O(1), checking for presence in the queue via C O(1)
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| − | - If W's degree is 2 and W is not in queue Q, add W to Q
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| − | </pre>--[[User:Bkarpov96|Bkarpov96]] ([[User talk:Bkarpov96|talk]]) 08:17, 7 July 2020 (UTC)
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