[BJOI 2018]染色

Posted 2020-12-27 akoasm

题意：求01成立。

并查集维护，记录一个变量判断决策。

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 4000010;
int f[maxn];
inline int find(int x){
    return x == f[x]?x : f[x] = find(f[x]);
}
signed main()
{
    ios::sync_with_stdio(false);
    int T;
    cin >> T;
    while(T--){
        int n,m;
        cin >> n >> m;
        int tag = (m < n + 2);
        for(int i = 1;i <= (n << 1); ++i){
            f[i] = i;
        }
        for(int i = 1;i <= m; ++i){
            int x,y;
            cin >> x >> y;
            f[find(x)] = find(y + n);
            f[find(y)] = find(x + n);
        }
        for(int i = 1;i <= n && tag; ++i){
            tag &= (find(i) != find(i + n));
        }
        if(tag) puts("YES");
        else puts("NO");
    }
    return 0;
}