Number of Provinces
给一个无向图, 求几个强连通组件.
并查集的例题.
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class Solution { public int findCircleNum(int[][] isConnected) { int size = isConnected.length; DSU dsu = new DSU(size); for(int i = 0; i < isConnected.length; i++) { for(int j = 0; j < isConnected.length; j++) { if(isConnected[i][j] == 1){ dsu.union(i, j); } } } Set<Integer> set = new HashSet<>(); for(int i = 0; i < size; i++) { set.add(dsu.get(i)); } return set.size(); } class DSU{ int[] p; public DSU(int size) { this.p = new int[size]; for(int i = 0; i < size; i++) { p[i] = i; } } int get(int v) { if(p[v] == v) return v; return p[v] = get(p[v]); } boolean union(int a, int b) { a = get(a); b = get(b); if(a == b) return false; p[a] = b; return true; } } } |