搜索与图论：染色法判别二分图

题目描述

输入样例

4 4
1 3
1 4
2 3
2 4

输出样例

Yes

参考代码

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

using namespace std;

const int N = 100010, M = 200010;

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; 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;
            }
        }
        
    if (flag) puts("Yes");
    else puts("No");
    
    return 0;
}