HDU 1272 小希的迷宫 （并查集判断回路、连通）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1272

数据的读入有些奇葩...题意就是给一个图，若有环或者不连通输出No，否则Yes。

参考博客：http://www.cnblogs.com/kuangbin/archive/2012/07/29/2613781.html

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <vector>#include <cctype>using namespace std;int f[100100], p[100100], book[100100];//  父节点     已出现的点   //该点是否出现过 int find(int t) {if(f[t] == 0) return t;return f[t] = find(f[t]);}int main () {int a, b;while(scanf("%d %d", &a, &b)) {memset(p, 0, sizeof(p));memset(book, 0, sizeof(book));memset(f, 0, sizeof(f));if(a == -1 && b == -1) break;if(a == 0 && b == 0) {  //一个空图居然是Yes... printf("Yes\n");continue;}f[a] = b;int cnt = 0;p[cnt++] = a;p[cnt++] = b;book[a] = 1, book[b] = 1;int flag = 0;while(scanf("%d %d", &a, &b)) {if(a == 0 && b == 0) break;if(flag) continue;int t1 = find(a);int t2 = find(b);if(t1 == t2) {  //说明有环，直接退出即可 flag = 1;continue;}f[t1] = t2;if(book[a] == 0) {book[a] = 1;p[cnt++] = a;}if(book[b] == 0) {book[b] = 1;p[cnt++] = b;}}if(flag == 0) {  //无环，判断是否连通 int num = 0;int i;for(i = 0; i < cnt; i++) {if(f[p[i]] == 0) {num++;}}if(num > 1) flag = 1;}if(flag) printf("No\n");else printf("Yes\n");}return 0;}