POJ1273（最大流）

Dinic算法的基本實現

#include <iostream>
#include <algorithm>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <cstring>
#include <vector>
#include <set>
#include <cmath>
#define LL long long
#define INF 0x3f3f3f3f
#define mod 1000000007
const int maxn = 100 + 5;
using namespace std;
int edge[250][250];//鄰接矩陣
int dis[250];//距源點距離，分層圖
int n,m;//n點數，M邊數
int bfs(int s, int e){//起點到終點
    queue<int> q;
    memset(dis, -1, sizeof(dis));
    dis[s] = 0;
    q.push(s);
    while(!q.empty()){
        int u = q.front(); q.pop();
        for(int i=1; i<=n; i++){
            if(dis[i] < 0 && edge[u][i] > 0){
                dis[i] = dis[u] + 1;
                q.push(i);
            }
        }
    }
    if(dis[e] > 0) return 1;
    return 0;
}
int dfs(int s, int e, int low){
    int a = 0;
    if(s == e) return low;
    for(int i=1; i<=n; i++){
        if(edge[s][i] > 0 && dis[i] == dis[s] + 1 && (a = dfs(i,e,min(low,edge[s][i])))){
            //聯通， 是分層圖的下一層， 能達到匯點
            edge[s][i] -= a;
            edge[i][s] += a;
            return a;
        }
    }
    return 0;
}
int main(){
    while(scanf("%d%d",&m,&n) == 2){
        memset(edge,0,sizeof(edge));
        for(int i=1; i<=m; i++){
            int f,t,flow;
            scanf("%d%d%d",&f,&t,&flow);
            edge[f][t] += flow;
        }
        int ans = 0;
        int sum = 0;
        while(bfs(1,n)){
            while((sum = dfs(1,n,INF))) ans += sum;
        }
        printf("%d\n",ans);
    }
    return 0;
}