染色法求二分图

#include<cstring>
#include<iostream>
#include<algorithm>

using namespace std;

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

int n, m;
int h[N], e[M], ne[M], idx;
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 false;
}

int main() {
    cin >> n >> m;
    memset(h, -1, sizeof h);

    while(m --) {
        int a, b;
        cin >> 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 = true;
                break;
            }
        }

    if(flag) puts("Yes");
    else puts("No");

    return 0;
}