UVA - 820 Internet Bandwidth（最大流模板题）

题目：

思路：

直接套最大流的模板就OK了，注意一下输出的格式。

代码：

#include <bits/stdc++.h>
#define inf 0x3f3f3f3f
#define MAX 1000000000
#define mod 1000000007
#define FRE() freopen("in.txt","r",stdin)
#define FRO() freopen("out.txt","w",stdout)
using namespace std;
typedef long long ll;
typedef pair<int,ll> pii;
const int maxn = 105;
int n;
struct Edge {
    int from,to,cap,flow;
    Edge(int from,int to,int cap,int flow):from(from),to(to),cap(cap),flow(flow) {}
};

struct Dinic {
    int n,m,s,t;
    vector<Edge> edges;
    vector<int> G[maxn];
    bool vis[maxn];
    int d[maxn];
    int cur[maxn];
    void init(){
        for(int i=0; i<maxn; i++){
            G[i].clear();
        }
        edges.clear();
    }

    void AddEdge(int from,int to,int cap) {
        edges.push_back(Edge(from,to,cap,0));
        edges.push_back(Edge(to,from,0,0));
        m = edges.size();
        G[from].push_back(m-2);
        G[to].push_back(m-1);
    }
    bool BFS(){
        memset(vis,0,sizeof(vis));
        queue<int>que;
        que.push(s);
        d[s] = 0;
        vis[s] = 1;
        while(!que.empty()){
            int x = que.front(); que.pop();
            for(int i=0; i<G[x].size(); i++){
                Edge& e = edges[G[x][i]];
                if(!vis[e.to] && e.cap>e.flow){
                    vis[e.to] = 1;
                    d[e.to] = d[x]+1;
                    que.push(e.to);
                }
            }
        }
        return vis[t];
    }

    int DFS(int x,int a){
        if(x == t || a==0) return a;
        int flow = 0,f;
        for(int i=cur[x]; i<G[x].size(); i++){
            Edge&e = edges[G[x][i]];
            if(d[x]+1 == d[e.to] && (f=DFS(e.to,min(a,e.cap-e.flow)))>0){
                e.flow += f;
                edges[G[x][i]^1].flow -= f;
                flow += f;
                a -= f;
                if(a==0) break;
            }
        }
        return flow;
    }

    int MaxFlow(int s,int t){
        this->s = s; this->t = t;
        int flow = 0;
        while(BFS()){
            memset(cur,0,sizeof(cur));
            flow += DFS(s,inf);
        }
        return flow;
    }
}dic;

int main(){
    int kase = 0;
    while(scanf("%d",&n) && n){
        dic.init();
        int ss,tt,cc,s,t,c;
        scanf("%d%d%d",&ss,&tt,&cc);
        for(int i=0; i<cc; i++){
            scanf("%d%d%d",&s,&t,&c);
            dic.AddEdge(s,t,c);
            dic.AddEdge(t,s,c);
        }
        int ans = dic.MaxFlow(ss,tt);
        printf("Network %d\n",++kase);
        printf("The bandwidth is %d.\n\n",ans);
    }
    return 0;
}