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+10;
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=1; i<=m; i++){
        pre[i]=-1;
    }
    pre[src]=0;
    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=1; i<=m; i++){
            if(i!=src&&capacity[indx][i]>0&&pre[i]==-1){
                pre[i]=indx;
                flow[i]=min(capacity[indx][i], flow[indx]);
                q.push(i);
            }
        }
    }
    if(pre[des]==-1) return -1;
    return flow[des];
}

int edmond_karp(int src, int des){
    int increasement=0;
    int sumflow=0;
    while((increasement=bfs(src, des))!=-1){
        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, 0, sizeof(capacity));
        memset(flow, 0, sizeof(flow));
        for(int i=0; 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
", edmond_karp(1, m));
    }
    return 0;
}