染色法判定二分图 -2025/11/12

染色法判定二分图

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

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

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

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

bool dfs(int u, int x){
	color[u] = x;
	for(int i = h[u]; i != -1; i = ne[i]){
		int j = e[i];
		if(!color[j]){
			if(!dfs(j, 3 - x)) return false;
		}
		else if(color[j] == x) return false;
	}
	return true;
}

int main(){
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	
	memset(h , -1 , sizeof h);
	
	cin >> n >> m;
	while(m --){
		int a, b;
		cin >> a >> b;
		add(a,b), add(b ,a);
	}
	
	int res = 0;
	int flag = 0;
	for(int i = 1; i <= n; i++){
		if(!color[i]){
			if(!dfs(i , 1)) {
				flag = 1;
				break;
			}
		}
	}
	
	if(flag) puts("No");
	else puts("Yes");
	return 0;
}