Hdu_2444 The Accomodation of Students -二分图判断+最大匹配

题意：先判断学生能否分成两块互不认识的集体，然后找出这两块集体的最大匹配

吐槽：迷之WA了几次，后来把判断是否是二分图弄成函数写在外面就ok了。

/************************************************
Author        :DarkTong
Created Time  :2016/8/1 13:02:46
File Name     :Hdu_2444.cpp
*************************************************/

//#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;
const int maxn = 200 + 10;
int w[maxn][maxn], n, m;
int Left[maxn];
bool used[maxn];
bool match(int i)
{
    for(int j=1;j<=m;++j) if(w[i][j]&&!used[j])
    {
        used[j] = true;
        if(!Left[j]||match(Left[j]))
        {
            Left[j] = i;
            return true;
        }
    }
    return false;
}
//返回最大匹配数
int hungary()
{
    int res=0;
    memset(Left, 0, sizeof(Left));
    for(int i=1;i<=n;++i)
    {
        memset(used, 0, sizeof(used));
        if(match(i)) res++;
    }
    return res;
}
int vis[maxn];
bool bfs()
{
    memset(vis, 0, sizeof(vis));
    for(int i=1;i<=n;++i)
    {
        if(!vis[i])
        {
            queue<int> q;
            q.push(i);
            vis[i] = 1;
            while(!q.empty())
            {
                int t = q.front(); q.pop();
                for(int j=1;j<=n;++j)
                {
                    if(w[t][j])
                    {
                        if(vis[j]==vis[t]) return false;
                        else if(vis[j]==0)
                        {
                            vis[j] = - vis[t];
                            q.push(j);
                        }
                    }
                }
            }
        }
    }
    return true;
}

int main()
{
    int T, cas=1, k;
    while(scanf("%d%d", &n, &k)==2)
    {
        memset(w, 0, sizeof(w));
        memset(vis, 0, sizeof(vis));
        m=n;

        int u, v;
        for(int i=1;i<=k;++i)
        {
            scanf("%d%d", &u, &v);
            w[v][u] = w[u][v]=1;
        }

        if(!bfs())
        {
            puts("No");
            continue;
        }

        int ans = hungary();
        printf("%d\n", ans>>1);
    }

    return 0;
}