zoukankan      html  css  js  c++  java
  • (网络流Dinic) poj 1273

    Drainage Ditches
    Time Limit: 1000MS   Memory Limit: 10000K
    Total Submissions: 58607   Accepted: 22508

    Description

    Every time it rains on Farmer John's fields, a pond forms over Bessie's favorite clover patch. This means that the clover is covered by water for awhile and takes quite a long time to regrow. Thus, Farmer John has built a set of drainage ditches so that Bessie's clover patch is never covered in water. Instead, the water is drained to a nearby stream. Being an ace engineer, Farmer John has also installed regulators at the beginning of each ditch, so he can control at what rate water flows into that ditch. 
    Farmer John knows not only how many gallons of water each ditch can transport per minute but also the exact layout of the ditches, which feed out of the pond and into each other and stream in a potentially complex network. 
    Given all this information, determine the maximum rate at which water can be transported out of the pond and into the stream. For any given ditch, water flows in only one direction, but there might be a way that water can flow in a circle. 

    Input

    The input includes several cases. For each case, the first line contains two space-separated integers, N (0 <= N <= 200) and M (2 <= M <= 200). N is the number of ditches that Farmer John has dug. M is the number of intersections points for those ditches. Intersection 1 is the pond. Intersection point M is the stream. Each of the following N lines contains three integers, Si, Ei, and Ci. Si and Ei (1 <= Si, Ei <= M) designate the intersections between which this ditch flows. Water will flow through this ditch from Si to Ei. Ci (0 <= Ci <= 10,000,000) is the maximum rate at which water will flow through the ditch.

    Output

    For each case, output a single integer, the maximum rate at which water may emptied from the pond.

    Sample Input

    5 4
    1 2 40
    1 4 20
    2 4 20
    2 3 30
    3 4 10
    

    Sample Output

    50
    #include<iostream>
    #include<cstdio>
    #include<cstring>
    #include<string>
    #include<cstdlib>
    #include<cmath>
    #include<algorithm>
    #include<queue>
    using namespace std;
    #define INF 0x7fffffff
    queue<int> q;
    int tab[250][250];
    int dis[250];
    int N,M,ANS;
    int BFS()
    {
         memset(dis,-1,sizeof(dis));
         dis[1]=0;
         q.push(1);
         while (!q.empty())
         {
               int x=q.front();
               q.pop();
               for (int i=1;i<=N;i++)
                   if (dis[i]<0&&tab[x][i]>0)
                   {
                      dis[i]=dis[x]+1;
                      q.push(i);
                   }
         }
         if(dis[N]>0)
            return 1;
         else
            return 0;
    }
    int find(int x,int low)
    {
        int a=0;
        if (x==N)return low;
        for (int i=1;i<=N;i++)
        if (tab[x][i]>0&&dis[i]==dis[x]+1&&(a=find(i,min(low,tab[x][i]))))
        {
           tab[x][i]-=a;
           tab[i][x]+=a;
           return a;
        }
        return 0;
    }
    int main()
    {
        int f,t,flow,tans;
        while(scanf("%d%d",&M,&N)!=EOF)
        {
                memset(tab,0,sizeof(tab));
                for(int i=1;i<=M;i++)
                {
                      scanf("%d%d%d",&f,&t,&flow);
                      tab[f][t]+=flow;
                }
                ANS=0;
                while(BFS())
                {
                      while(tans=find(1,INF))ANS+=tans;
                }
                printf("%d
    ",ANS);
        }
        return 0;
    }
    

      

      

  • 相关阅读:
    一道leetcode题的收获如何比较字符串的大小重写sort中的compare[](string &s,string &t){return s+t>t+s};
    unsigned int表示负数问题
    fork()和printf()几点注意细节
    32位机中数据问题
    C++隐藏机制
    ||,&&,++i解答
    enum忽略知识点
    硬链接与软链接
    20145215实验五 Java网络编程及安全
    证书与keytool
  • 原文地址:https://www.cnblogs.com/a972290869/p/4249227.html
Copyright © 2011-2022 走看看