染色法判定二分图板子

染色法判定二分图

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10, M = N * 2;

int n, m;
int h[N], e[M], ne[M], idx;
bool st[N];
int color[N];

void add(int a, int b){
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}

bool dfs(int u, int c){
    color[u] = c;
    for(int i = h[u]; i != -1; i = ne[i]){
        int j = e[i];
        if(!color[j]){
            if(!dfs(j, 3 - c)) return false;
        }else if(color[j] == c) return false;
    }
    return true;
}
signed main(){
    memset(h, -1, sizeof h);
    scanf("%d%d", &n, &m);
    
    while(m--){
        int a, b; scanf("%d%d", &a, &b);
        add(a, b); add(b, a);
    }
    
    bool flag = true;
    for(int i = 1; i <= n; ++i){
        if(!color[i]){
            if(!dfs(i, 1)) {flag = false; break;}
        }
    }
    
    if(flag) puts("Yes");
    else puts("No");
    
    return 0;
}