HDU ACM 1532 Drainage Ditches(网络流---增广路)

 

http://acm.hdu.edu.cn/showproblem.php?pid=1532

题意:找到从起点到终点的最大流.

　　　　　　BFS（）---- 找到一条增广路

　　　　　　GetFlow()---- 找到该增广路的流量,即流量最小的边,减去流量,再在增广路的个边上补反边

#include <iostream>
#include <queue>
using namespace std;
const int MAX = 200 + 10;
const int INF = 0x3fffffff;

bool used[MAX];
int front[MAX];
int map[MAX][MAX];
int n;
int m;
int sumflow;
bool BFS(int s){//用广搜找增广路
    queue <int> q;
    memset(used,0,sizeof(used));
    q.push(s);
    front[s] = 1;
    used[s] = 1;
    while(!q.empty()){
        int mid = q.front();
        q.pop();
        int i;
        for(i=1;i<=n;i++){
            if(!used[i] && map[mid][i] > 0){
                q.push(i);
                used[i] = 1;
                front[i] = mid;
                if(i == n){
                    return 1;
                }
            }
        }
    }
    return 0;
}
int GetFlow(){
    int min = INF;
    int i = n;
    while(front[i] != i){
        if(map[front[i]][i] < min){
            min = map[front[i]][i];
        }
        i = front[i];
    }

    i = n;
    while(front[i] != i){
        map[front[i]][i] -= min;
        map[i][front[i]] += min;
        i = front[i];
    }
    return min;
}
int CalSum(){
    while(BFS(1)){
        sumflow += GetFlow();
    }
    return sumflow;
}



int main(){
    while(cin>>m>>n){
        sumflow = 0;
        memset(map,0,sizeof(map));
        int i;
        for(i=0;i<m;i++){
            int a,b,c;
            cin>>a>>b>>c;
            map[a][b] += c;//注意这里   map[a][b] = c   会错
        }
        cout<<CalSum()<<endl;
    }
    return 0;
}