HDU 2444 The Accomodation of Students（二分图判定+最大匹配）

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<cmath>
#include<map>
#include<stack>
#include<set>
using namespace std;
#define REPF( i , a , b ) for ( int i = a ; i <= b ; ++ i )
#define REP( i , n ) for ( int i = 0 ; i < n ; ++ i )
#define CLEAR( a , x ) memset ( a , x , sizeof a )
typedef long long LL;
typedef pair<int,int>pil;
const int maxn=220;
int mp[maxn][maxn];
int vis[maxn],col[maxn];
int used[maxn],link[maxn];
int n,m,flag;
bool bfs(int x)
{
    queue<int>q;
    q.push(x);
    col[x]=1;
    while(!q.empty())
    {
        int xx=q.front();
        q.pop();
        REPF(i,1,n)
        {
            if(mp[xx][i]&&col[i]==-1)
            {
                q.push(i);
                col[i]=!col[xx];
            }
            if(mp[xx][i]&&col[i]==col[xx])
                return false;
        }
    }
    return true;
}
bool ok()
{
    flag=0;
    REPF(i,1,n)
    {
        if(col[i]==-1&&!bfs(i))
        {
            flag=1;
            break;
        }
    }
    if(flag) return false;
    return true;
}
bool dfs(int x)
{
    REPF(i,1,n)
    {
        if(mp[x][i]&&!used[i])
        {
            used[i]=1;
            if(link[i]==-1||dfs(link[i]))
            {
                link[i]=x;
                return true;
            }
        }
    }
    return false;
}
void work()
{
    CLEAR(link,-1);
    int res=0;
    REPF(i,1,n)
    {
        CLEAR(used,0);
        if(dfs(i)) res++;
    }
    printf("%d\n",res>>1);
}
int main()
{
    int x,y;
    while(~scanf("%d%d",&n,&m))
    {
        CLEAR(col,-1);
        CLEAR(mp,0);
        REP(i,m)
        {
            scanf("%d%d",&x,&y);
            mp[x][y]=mp[y][x]=1;
        }
        if(!ok())  puts("No");
        else  work();
    }
    return 0;
}