【染色法判断二分图】AcWing860.染色法判定二分图

AcWing860.染色法判定二分图

题解

若出现奇数环，染色一定矛盾
当前点没有染色，就染色包括其子节点

#include <iostream>
#include <cstring>
#include <cstdio>

using namespace std;

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

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

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

bool dfs(int u, int c)
{
    color[u] = c;
    for(int i = h[u]; ~i; 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()
{
    memset(h, -1, sizeof h);
    scanf("%d%d",&n,&m);
    int a, b;
    for(int i = 0; i < m; ++i)
    {
        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;
            }
        }
            
    }
    printf("%s\n",flag?"Yes":"No");
    return 0;
}