HDU3549 Flow Problem【網路流 最大流】
Flow Problem
Time Limit: 5000/5000 MS (Java/Others) Memory Limit: 65535/32768 K (Java/Others)
Total Submission(s): 23036 Accepted Submission(s): 10756
Problem Description
Network flow is a well-known difficult problem for ACMers. Given a graph, your task is to find out the maximum flow for the weighted directed graph.
Input
The first line of input contains an integer T, denoting the number of test cases.
For each test case, the first line contains two integers N and M, denoting the number of vertexes and edges in the graph. (2 <= N <= 15, 0 <= M <= 1000)
Next M lines, each line contains three integers X, Y and C, there is an edge from X to Y and the capacity of it is C. (1 <= X, Y <= N, 1 <= C <= 1000)
Output
For each test cases, you should output the maximum flow from source 1 to sink N.
Sample Input
2
3 2
1 2 1
2 3 1
3 3
1 2 1
2 3 1
1 3 1
Sample Output
Case 1: 1
Case 2: 2
Author
HyperHexagon
問題連結:HDU3549 Flow Problem
問題描述:給你一個N個頂點M條邊的有向圖,要你求1號點到N號點的最大流。
解題思路:最大流模板題,使用EdmondsKarp演算法(鄰接矩陣形式)
Source
HyperHexagon's Summer Gift (Original tasks)
AC的C++程式:
#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int N=20;
const int INF=0x3f3f3f3f;
int g[N][N];
int pre[N];
bool vis[N];
int n,m;
int EdmondsKarp()
{
queue<int>q;
memset(pre,-1,sizeof(pre));
memset(vis,false,sizeof(vis));
vis[1]=true;
pre[1]=0;
q.push(1);
int v;
bool flag=false;
while(!q.empty())
{
v=q.front();
q.pop();
for(int i=1;i<=n;i++)
if(g[v][i]>0&&!vis[i])
{
pre[i]=v;
vis[i]=true;
if(i==n)
{
flag=true;
break;
}
else
q.push(i);
}
}
if(!flag)//找不到就返回
return 0;
int ans=INF;
for(v=n;v!=1;v=pre[v])
ans=min(ans,g[pre[v]][v]);
for(v=n;v!=1;v=pre[v])
{
g[pre[v]][v]-=ans;
g[v][pre[v]]+=ans;
}
return ans;
}
int main()
{
int T;
scanf("%d",&T);
for(int t=1;t<=T;t++)
{
scanf("%d%d",&n,&m);
int a,b,c;
memset(g,0,sizeof(g));
for(int i=1;i<=m;i++)
{
scanf("%d%d%d",&a,&b,&c);
g[a][b]+=c;
}
int ans=0,temp;
while(temp=EdmondsKarp())
ans+=temp;
printf("Case %d: %d\n",t,ans);
}
return 0;
}