【HDU】 1532 Drainage Ditches

Drainage Ditches

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题目链接

• Drainage Ditches

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题目大意

给你一个有向图，要求求出从1到m的最大流。

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题解

上面已经说的很清楚了，就是求出1到m的最大流即可。

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代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>

using namespace std;

int u,v,dist,a[205][205],flow[205],pre[205],q[205],n,m;


int bfs(int s,int des)
{
    memset(q,0,sizeof(q));
    memset(pre,0,sizeof(pre));
    int h=0,t=0;
    q[h++]=s; flow[s]=0x7fffffff;
    pre[s]=s; flow[des]=0;
    while (h!=t)
    {
        int u=q[t];
        if (u==des) break;
        for (int v=1;v<=m;v++) if (a[u][v]>0 && !pre[v])
        {
            q[h++]=v; pre[v]=u;
            flow[v]=min(flow[u],a[u][v]);
        }
        t++;
    }
    return flow[des];
}

int maxflow(int s,int des)
{
    int t,ans=0;
    while(t=bfs(s,des),t!=0)
    {
        for (int i=des;i!=s;i=pre[i])
        {
            a[pre[i]][i]-=t;
            a[i][pre[i]]+=t;
        }
        ans+=t;
    }
    return ans;
}

int main()
{
    while (scanf("%d%d",&n,&m)!=EOF)
    {
        memset(a,0,sizeof(a));
        for (int i=1;i<=n;i++)
        {
            scanf("%d%d%d",&u,&v,&dist);
            a[u][v]+=dist;
        }
        int ans=maxflow(1,m);
        printf("%d\n",ans);
    }
    return 0;
}