题目链接:
http://acm.hdu.edu.cn/showproblem.php?pid=3549
题目大意:
给你一个N个节点M条边的加权有向图,源点为1,汇点为N,求此图的最大流。
思路:
这道题就是网络流求最大流的裸题。直接用Edmond-Karp算法来做就可以了。
AC代码:
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const int MAXN = 20;
const int MAXM = 2020;
int Map[MAXN][MAXN],pre[MAXN],N,M;
bool EkBFS(int start,int end)
{
queue<int> Q;
bool vis[MAXN];
memset(vis,false,sizeof(vis));
memset(pre,-1,sizeof(pre));
Q.push(start);
vis[start] = true;
while(!Q.empty())
{
int u = Q.front();
if(u == end)
return true;
Q.pop();
for(int i = 0; i <= N; ++i)
{
if(Map[u][i] && !vis[i])
{
vis[i] = true;
pre[i] = u;
Q.push(i);
}
}
}
return false;
}
int EkMaxFlow(int start,int end)
{
int v,Ans = 0,MinN;
while(EkBFS(start,end))
{
MinN = 0xffffff0;
v = end;
while(pre[v] != -1)
{
MinN = min(MinN,Map[pre[v]][v]);
v = pre[v];
}
Ans += MinN;
v = end;
while(pre[v] != -1)
{
Map[pre[v]][v] -= MinN;
Map[v][pre[v]] += MinN;
v = pre[v];
}
}
return Ans;
}
int main()
{
int T,u,v,w, kase = 0;
scanf("%d", &T);
while(T--)
{
memset(Map,0,sizeof(Map));
scanf("%d%d",&N,&M);
for(int i = 0; i < M; ++i)
{
scanf("%d%d%d",&u,&v,&w);
Map[u][v] += w;
}
printf("Case %d: %d\n",++kase, EkMaxFlow(1,N));
}
return 0;
}