[最大流/Edmonds-karp算法]hiho1369 网络流一

hiho1369
网络流一

题意：

最大交通车流量

思路：

裸的Edmonds_karp算法，请套模板

代码：

/**************************************************************
Problem: hiho_1369
User: soundwave
Language: C++
Result: Accepted
Time: 24ms
Memory: 1MB
****************************************************************/
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <stdio.h>
#include <queue>
#include <vector>
#include <cmath>
#include <string.h>
//注意重边
using namespace std;
const int maxn = 500+5;
const int INF = 1<<29;
int my_min(int x, int y){
return x<y?x:y;
}
struct Edge{
int from, to;
int cap, flow;
Edge(int u, int v, int c, int f): from(u), to(v), cap(c), flow(f) {}
};
struct Edmonds_karp{
int n, m;
vector<Edge> edges;
vector<int> G[maxn];
int path[maxn];
int a[maxn];
void init(int n){
for(int i=0; i<n; 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);
}
int MaxFlow(int s, int t){
int re = 0;
while(1){
queue<int> Q;
Q.push(s);
memset(a,0,sizeof(a));
a[s] = INF;
//bfs找增广路
while(!Q.empty()){
int u = Q.front();
Q.pop();
for(int i=0; i<G[u].size(); i++){
Edge &v = edges[G[u][i]];
if(!a[v.to] && v.cap>v.flow){
path[v.to] = G[u][i];
Q.push(v.to);
a[v.to] = my_min(a[u], v.cap-v.flow);
}
}
if(a[t]) break;
}
if(!a[t]) break;//找不到增广路，当前的流量就是最大流
for(int u=t; u!=s; u=edges[path[u]].from){
edges[path[u]].flow += a[t];
edges[path[u]^1].flow -= a[t];
}
re += a[t];
}
return re;
}
};
int n,m;
Edmonds_karp EK;
int main(){
int x, y, val;
while(~scanf("%d%d", &n, &m)){
EK.init(n);
while(m-->0){
scanf("%d%d%d", &x, &y, &val);
EK.AddEdge(x,y,val);
}
x = EK.MaxFlow(1,n);
printf("%d\n", x);
}
return 0;
}