計蒜課/排澇(Edmond-Karp)

題目鏈接: https://nanti.jisuanke.com/t/36

題意:中文題目誒~

思路: 最大流模板題....

關於最大流算法blog:

　　http://www.cnblogs.com/zsboy/archive/2013/01/27/2878810.html

　　http://blog.csdn.net/y990041769/article/details/21026445

　　http://www.cnblogs.com/luweiseu/archive/2012/07/14/2591573.html

代碼:

 #include <iostream>
 #include <stdio.h>
 #include <queue>
 #include <string.h>
 using namespace std;

 const int MAXN=2e2+;
 const int inf=0x7fffffff;
 int capacity[MAXN][MAXN];//記錄殘留網絡流量
 int flow[MAXN]; //標記從源點到當前節點實際還剩多少流量可用
 int pre[MAXN]; //pre[i]爲i的父親節點
 int n, m;

 int bfs(int src, int des){
     queue<int> q;
     while(!q.empty()){
         q.pop();
     }
     for(int i=; i<=m; i++){
         pre[i]=-;
     }
     pre[src]=;
     flow[src]=inf;
     q.push(src);
     while(!q.empty()){
         int indx=q.front();
         q.pop();
         if(indx==des) break;//找到了增廣徑
         for(int i=; i<=m; i++){
             if(i!=src&&capacity[indx][i]>&&pre[i]==-){
                 pre[i]=indx;
                 flow[i]=min(capacity[indx][i], flow[indx]);
                 q.push(i);
             }
         }
     }
     if(pre[des]==-) return -;
     return flow[des];
 }

 int edmond_karp(int src, int des){
     int increasement=;
     int sumflow=;
     while((increasement=bfs(src, des))!=-){
         int k=des; //利用前區尋找路徑
         while(k!=src){
             int last=pre[k];
             capacity[last][k]-=increasement;//改變正向邊容量
             capacity[k][last]+=increasement;//改變反向邊容量
             k=last;
         }
         sumflow+=increasement;
     }
     return sumflow;
 }

 int main(void){
     int start, end, ci;
     while(~scanf("%d%d", &n, &m)){
         memset(capacity, , sizeof(capacity));
         memset(flow, , sizeof(flow));
         for(int i=; i<n; i++){
             scanf("%d%d%d", &start, &end, &ci);
             if(start==end) continue;
             capacity[start][end]+=ci;//可能有重邊
         }
         printf("%d\n", edmond_karp(, m));
     }
     return ;
 }