【网络流】POJ1273 Drainage Ditches

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define inf 1<<30
using namespace std;

struct edge{
    int to,ne,cap;
}e[400005];

int n,m,s,t,a,b,c,ans,ecnt;
int head[10005],layer[10005];
queue<int> q;

void add(int x,int y,int z)
{
    e[++ecnt].to=y;e[ecnt].cap=z;e[ecnt].ne=head[x];head[x]=ecnt;
    e[++ecnt].to=x;e[ecnt].cap=0;e[ecnt].ne=head[y];head[y]=ecnt;
}

bool bfs()
{
    //while(!q.empty())q.pop();
    q.push(s);
    for(int i=0;i<=m;++i)layer[i]=0;
    layer[s]=1;
    while(!q.empty())
    {
        int d=q.front();
        q.pop();
        for(int i=head[d];i;i=e[i].ne)
        {
            int dd=e[i].to;
            if(e[i].cap>0&&layer[dd]==0)
            {
                layer[dd]=layer[d]+1;
                q.push(dd);
            }
        }
    }
    return layer[t];
}

int dfs(int x,int val)
{
    if(val==0||x==t)return val;
    int ret=0;
    for(int i=head[x];i;i=e[i].ne)
    {
        int dd=e[i].to;
        if(e[i].cap>0&&layer[dd]==layer[x]+1)
        {
            int tmp=dfs(dd,min(val,e[i].cap));
            ret+=tmp;
            val-=tmp;
            e[i].cap-=tmp;
            e[(i-1)^1+1].cap+=tmp;
        }
    }
    return ret;
}

void dinic()
{
    while(bfs())
    {
        ans+=dfs(s,inf);
    }
}

int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        ecnt=0;ans=0;
        memset(head,0,sizeof(head));
        for(int i=1;i<=n;++i)
        {
            scanf("%d%d%d",&a,&b,&c); 
            add(a,b,c);
        }
        s=1;t=m;
        dinic();
        printf("%d\n",ans);
    }
}