hdu2444 二分图判定+匹配

判定一个图是否是二分图,可以将此图染色判定

首先取一个点染成白色，然后将其相邻的点染成黑色，如果发现有相邻且同色的点，那么就退出，可知这个图并非二分图。

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <string.h>
#include <string>

using namespace std;

const int MAXN = 200 + 10;

bool c[MAXN][MAXN], vis[MAXN], flag;
int match[MAXN], col[MAXN], n, m;

void init()
{
    memset(match, -1, sizeof(match));
    memset(c, false, sizeof(c));
    memset(col, 0, sizeof(col));
}

void dfa(int u, int val)
{
    for (int i = 1; i <= n; i++)
    {
        if (c[u][i])
        {
            if (col[i] == 0)
            {
                col[i] = -val;
                dfa(i, -val);
            }
            else if (val == col[i])
            {
                flag = false;
                return ;
            }
        }
    }
}

bool judge()
{
    flag = true;
    col[1] = 1;
    dfa(1, 1);

    return flag;
}

bool dfs(int u)
{
    for (int i = 1; i <= n; i++)
    {
        if (c[u][i] && !vis[i])
        {
            vis[i] = true;
            if (match[i] == -1 || dfs(match[i]))
            {
                match[i] = u;
                return true;
            }
        }
    }

    return false;
}

void input()
{
    int u, v;

    while (scanf("%d %d", &n, &m) != EOF)
    {
        init();

        for (int i = 0; i < m; i++)
        {
            scanf("%d %d", &u, &v);
            c[u][v] = c[v][u] = true;
        }

        if (!judge())
        {
            printf("No\n");
        }
        else
        {
            int ans = 0;

            for (int i = 1; i <= n; i++)
            {
                memset(vis, false, sizeof(vis));
                if (dfs(i))
                {
                    ans++;
                }
            }

            cout << ans / 2 << endl;
        }
    }
}

int main()
{
    input();
    return 0;
}