这是本蒟蒻写的判二分图，问一下，哪里错了。

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

using namespace std;
const int N = 100010, M = 200010;

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

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;
}

int main(){
    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);
    
    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;
            }
    
    puts(flag ? "Yes" : "No");
        
    return 0;
}