hdu1532 Drainage Ditches--最大流ek

原题链接： ​​http://acm.hdu.edu.cn/showproblem.php?pid=1532​​

题意：

n条路，m个点，每条边一个流速，求最大流速，1是源点，m是汇点。

依旧模板题。

#define _CRT_SECURE_NO_DEPRECATE 

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<queue>

using namespace std;

int n, m;
int s, t;
int pre[205];
int vis[205];
int p[205][205];

bool bfs()
{
  memset(pre, 0, sizeof(pre));
  memset(vis, 0, sizeof(vis));
  vis[s] = 1;
  queue<int> Q;
  Q.push(s);

  while (!Q.empty())
  {
    int cur = Q.front();
    Q.pop();

    if (cur == t)
      return true;

    for (int i = 1; i <= n; i++)
    {
      if (!vis[i] && p[cur][i])
      {
        pre[i] = cur;
        vis[i] = 1;
        Q.push(i);
      }
    }
  }
  return false;
}

int maxFlow()
{
  int ans = 0;
  while (1)
  {
    if (!bfs())
      return ans;
    int minn = 99999999;
    for (int i = t; i != s; i = pre[i])
      minn = min(minn, p[pre[i]][i]);
    for (int i = t; i != s; i = pre[i])
    {
      p[pre[i]][i] -= minn;
      p[i][pre[i]] += minn;
    }
    ans += minn;
  }
}

int main()
{
  int u, v, w;
  while (~scanf("%d%d", &m, &n))
  {
    s = 1;
    t = n;
    memset(p, 0, sizeof(p));//注意这里要初始化

    for (int i = 1; i <= m; i++)
    {
      scanf("%d%d%d", &u, &v, &w);
      p[u][v] += w;
    }

    printf("%d\n", maxFlow());
  }
  return 0;
}