Day66：HDU3549 Flow Problem最大流模板题EK算法

求最大流模板题

用了EK算法，即bfs+max_flow

具体解析可以看我这篇博客https://www.cnblogs.com/OFSHK/p/12231765.html#_label3

AC代码：

#include<stdio.h>
#include<iostream>
#include<queue>
#include<string.h>
using namespace std;
#define inf 0x3f3f3f3f

const int N=20;
int e[N][N],s,t,m,n,pre[N];
bool book[N];

bool bfs()
{
//    memset(book,0,sizeof(book));
//    memset(pre,0,sizeof(pre));
    for(int i=0;i<=t;i++)
        book[i]=pre[i]=0;
    queue<int>Q;
    Q.push(s);
    book[s]=1;
    while(!Q.empty())
    {
        int u=Q.front();
        Q.pop();
        if(u==t)
            return 1;
        for(int i=1; i<=n; i++)
        {
            if(book[i]==0)
            {
                if(e[u][i])
                {
                    book[i]=1;
                    pre[i]=u;
                    Q.push(i);
                }
            }
        }
    }
    return 0;
}

int max_flow()
{
    int maxflow=0;
    while(bfs())
    {
//        if(bfs()==0)
//            return maxflow;
        int minn=inf;
        for(int i=t; i!=s; i=pre[i])
            minn=min(minn,e[pre[i]][i]);
        for(int i=t; i!=s; i=pre[i])
        {
            e[pre[i]][i]-=minn;
            e[i][pre[i]]+=minn;
        }
        maxflow+=minn;
    }
    return maxflow;
}

int main()
{
    int u,v,w,tt=1,T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d %d",&n,&m);
        memset(e,0,sizeof(e));
        s=1,t=n;
        for(int i=1; i<=m; i++)
        {
            int u,v,w;
            scanf("%d %d %d",&u,&v,&w);
            e[u][v]+=w;
        }
        int ans=max_flow();
        printf("Case %d: %d\n",tt++,ans);
    }
    return 0;
}