poj 1273 Drainage Ditches

http://poj.org/problem?id=1273

题意：有一些流水的水沟，求从起点1到达终点的最大水量，每条水沟都有一个最大流水量；

思路：基础的网络流问题(EK算法),注意边的重复；

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define max 205
using namespace std;
int s[max][max] = {0};
int n = 0;
int m = 0;
int a = 0;
int b = 0;
int ss = 0;
void ek()
{
    int ans = 0;
    int pre[max] = {0};
    int flow[max] = {0};
    while(1)
    {
        memset(pre,0,sizeof(pre));
        memset(flow,0,sizeof(flow));
    queue<int>que;
    que.push(1);
    flow[1] = 99999999;
    while(!que.empty())
    {
        a=que.front();
        que.pop();
        for(int i =1;i <= m; ++i)
        if(!pre[i]&&s[a][i])
        {
        flow[i] = min(flow[a],s[a][i]);
        pre[i] = a;
        que.push(i);
        }

    }
    if(pre[m] == 0)
    break;
    ans += flow[m];
    for(int i = m; i != 1;i = pre[i])
    {
        s[pre[i]][i]-=flow[m];
        s[i][pre[i]]+=flow[m];
    }
    }
    printf("%d\n",ans);
}
int main()
{
    while(scanf("%d%d",&n,&m) != EOF)
    {
        memset(s,0,sizeof(s));
        for(int i = 1;i <= n ;++i)
        {
            scanf("%d%d%d",&a,&b,&ss);
            s[a][b] += ss;
        }
        ek();
    }
    return 0;
}