网络流—最大流（Edmond-Karp算法）

Posted 2020-10-10 爱国呐

占坑

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <queue>
using namespace std;
const int MAX=1000000;
int map[20][20],flow[20],pre[20],n,m;
bool vis[20];
int BFS()
{
    int up;
    queue<int> q;
    vis[1]=1;
    memset(pre,-1,sizeof(pre));
    memset(vis,0,sizeof(vis));
    for(int i=1; i<=n; i++)
        flow[i]=MAX;
    q.push(1);
    while(!q.empty())
    {
        up=q.front();
        q.pop();
        if(up==n)
            break;
        for(int i=1; i<=n; i++)
        {
            if(!vis[i]&&map[up][i]>0)
            {
                vis[i]=1;
                flow[i]=min(flow[up],map[up][i]);
                pre[i]=up;
                q.push(i);
            }
        }
    }
    if(!vis[n]||n==1)
        return -1;
    return flow[n];
}
int EK()
{
    int d,maxflow=0,up,down;
    maxflow=0;
    while((d=BFS())!=-1)
    {
        maxflow+=d;
        down=n;
        while(down!=1)
        {
            up=pre[down];
            map[up][down]-=d;
            map[down][up]+=d;
            down=up;
        }
    }
    return maxflow;
}
int main()
{
    int T,a,b,c,h=1,i;
    scanf("%d",&T);
    while(T--)//T组测试样例
    {
        memset(map,0,sizeof(map));
        scanf("%d%d",&n,&m);//n个点，m条边
        for(i=1; i<=m; i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            map[a][b]+=c;
        }
        printf("Case %d: %d\n",h++,EK());//输出从1到n号点的最大流
    }
    return 0;
}