CodeForces 690C1 Brain Network (easy) （水题，判断树）

#include <bits/stdc++.h>

using namespace std;
const int maxn =1000 + 5;
int p[maxn];

int Find(int x){  return x == p[x] ? x : p[x] = Find(p[x]); }

int main(){
    int n, m, x, y;
    cin >> n >> m;
    bool ok = true;
    for(int i = 1; i <= n; ++i)  p[i] = i;
    for(int i = 0; i < m; ++i){
        scanf("%d %d", &x, &y);
        x = Find(x);
        y = Find(y);
        if(x == y) ok = false;
        else p[y] = x;
    }

    if(ok && m == n-1)  puts("yes");
    else  puts("no");
    return 0;
}