[图论][二分图判断]The Accomodation of Students

#include <iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;

int n,m;
int Map[210][210];
int flag[210];
int used[210];
int vis[210];

bool bfs_judge(){//染色法判断是否为二分图
  for(int i=0;i<210;i++) flag[i]=-1;
  for(int i=1;i<=n;i++){
    if(flag[i]!=-1) continue;
    flag[i]=0;
    queue<int > q;
    q.push(i);//以还未被染过色的i点(还未被搜索过的点)为起始点展开bfs
    while(!q.empty()){
        int head=q.front();
        q.pop();
        for(int j=1;j<=n;j++){
            if(!Map[head][j]) continue;
            if(flag[j]!=-1&&flag[head]==flag[j]) return false;
            else if(flag[j]==-1){flag[j]=!flag[head]; q.push(j);}
        }
    }
  }
  return true;
}

bool match(int x){
   for(int i=1;i<=n;i++){
     if(!vis[i]&&Map[x][i]){
        vis[i]=1;
        if(!used[i]||match(used[i])){
            used[i]=x;
            return true;
        }
     }
   }
   return false;
}

int main()
{
    while(scanf("%d%d",&n,&m)!=EOF){
        memset(Map,0,sizeof(Map));
        for(int i=1;i<=m;i++){
            int a,b;
            scanf("%d%d",&a,&b);
            Map[a][b]=Map[b][a]=1;//无向图
        }
        if(bfs_judge()==false) {printf("No\n"); continue;}
        int ans=0;
        memset(used,0,sizeof(used));
        for(int i=1;i<=n;i++){
            memset(vis,0,sizeof(vis));
            if(match(i)) ans++;
        }
        printf("%d\n",ans/2);//每一对匹配被计算了两次
    }
    return 0;
}