Geeks - Union-Find Algorithm - Detect Cycle in a an Undirected Graph算法

利用Union Find的方法查找图中是否有环。

在于构建一个图数据结构，和一般图的数据结构不同的是这个图是记录了边的图，并在查找过程中不断把边连接起来，形成一个回路。

原文地址：

http://www.geeksforgeeks.org/union-find/

#pragma once#include <stdio.h>#include <stdlib.h>#include <string.h>#include <algorithm>class UnionFind{struct Edge{int src, des;explicit Edge(int s = 0, int d = 0) : src(s), des(d) {}};struct Graph{int V, E; // V-> Number of vertices, E-> Number of edgesEdge *edges;Graph(int v, int e) : V(v), E(e), edges(new Edge[e]){}~Graph(){if (edges) delete [] edges;}};int find(int parent[], int i){if (-1 == parent[i]) return i;return find(parent, parent[i]);}void unionTwo(int parent[], int x, int y){int xset = find(parent, x);int yset = find(parent, y);parent[xset] = yset;}bool isCycle(Graph *gra){int *parent = (int *) malloc (gra->V * sizeof(int));std::fill(parent, parent+gra->V, -1);for (int i = 0; i < gra->E; i++){int x = find(parent, gra->edges[i].src);int y = find(parent, gra->edges[i].des);if (x == y) return true;unionTwo(parent, x, y);}return false;}public:UnionFind(){Graph *gra = new Graph(3, 3);gra->edges[0].src = 0;gra->edges[0].des = 1;gra->edges[1].src = 1;gra->edges[1].des = 2;gra->edges[2].src = 0;gra->edges[2].des = 2;if (isCycle(gra))printf( "Graph contains cycle\n" );elseprintf( "Graph doesn't contain cycle\n" );delete gra;}};