題意：就是求最大匹配

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<set>
#include<map>
#include<string>
#include<cstring>
#include<stack>
#include<queue>
#include<vector>
#include<limits>
#include<ctime>
 

#include<cassert>
#include<cstdlib>
#define lson (rt<<1),L,M
#define rson (rt<<1|1),M+1,R
#define M ((L+R)>>1)
#define cl(a,b) memset(a,b,sizeof(a));
#define LL long long
#define P pair<int,int>
#define X first
#define Y second
#define pb push_back
#define fread(a) freopen(a,"r",stdin);
 

#define fwrite(a) freopen(a,"w",stdout);
using namespace std;
const int maxn=5005;
const int inf=999999;

vector<int> G[maxn];
int matching[maxn];
bool vis[maxn];
int num;
bool dfs(int u){
    int N=G[u].size();
    for(int i=0;i<N;i++){
        int v=G[u][i];
        if(vis[v])continue;
        vis[v]=true
 
;
        if(matching[v]==-1||dfs(matching[v])){
            matching[v]=u;
            return true;
        }
    }
    return false;
}
int hungar(){
    int ans=0;
    cl(matching,-1);
    for(int i=0;i<num;i++){
        cl(vis,false);
        if(dfs(i))ans++;
    }
    return ans/2;//無向邊，算了所有。除2
}


int main(){
    int T;
    scanf("%d",&T);
    while(T--){
        int n;
        scanf("%d",&n);
        for(int i=0;i<=n;i++)G[i].clear();
        int m=n*3/2;
        while(m--){
            int x,y;
            scanf("%d%d",&x,&y);
            x--;y--;
            G[x].pb(y);//這裏是無向邊
            G[y].pb(x);
        }
        num=n;
        int ans=hungar();
        printf("%d\n",ans);
    }
    return 0;
}

HDU1845Jimmy’s Assignment（無向圖，最大匹配）