hihoCoder 树结构判定（并查集）

#include <stdio.h>
#include<string.h>
const int maxn = 500+5;
int par[maxn];
int T, n, m;

void init() {
for(int i = 0; i <= n; i++) {
par[i] = i;
}
}

int findRoot(int x) {
return x == par[x] ? x : par[x] = findRoot(par[x]);
}

int main() {
scanf("%d", &T);
while(T--) {
scanf("%d%d", &n, &m);
init();
int u, v;
for(int i = 0; i < m; i++) {
scanf("%d%d", &u, &v);
int x = findRoot(u);
int y = findRoot(v);
if(x != y) {
par[x] = y;
}
}

bool ok = 1;
if(n-1 != m) ok = 0;
//判断是否所有点连通
if(ok) {
int root = findRoot(1);
for(int i = 2; i <= n; i++) {
if(findRoot(i) != root) {
ok = 0;
break;
}
}
}

if(ok) printf("YES\n");
else printf("NO\n");

}
return 0;
}