题目链接
http://acm.hdu.edu.cn/showproblem.php?pid=3452
这道题就是说是树其实是图,把最终的叶子和一个超级汇点一连,用根结点和超级汇点跑最小割就行
#include <bits/stdc++.h>
using namespace std;
int n, m;
const int maxn = 1005;
const int INF = 0x3f3f3f3f;
struct Edge
{
int from, to, cap, flow;
Edge(int u, int v, int c, int f):from(u), to(v), cap(c), flow(f) {}
};
struct EdmondsKarp
{
vector<int>G[maxn];
vector<Edge>edges;
int a[maxn];
int p[maxn];
void init(int n)
{
for(int i = 0;i <= n + 1;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));
int m = edges.size();
G[from].push_back(m - 2);
G[to].push_back(m - 1);
}
int MaxFlow(int s, int t)
{
int flow = 0;
for(;;)
{
queue<int> Q;
Q.push(s);
memset(a, 0, sizeof(a));
a[s] = INF;
while(!Q.empty())
{
int x = Q.front();
Q.pop();
for(int i = 0;i < (int)G[x].size();i++)
{
Edge &e = edges[G[x][i]];
if(!a[e.to]&&e.cap > e.flow)
{
p[e.to] = G[x][i];
a[e.to] = min(a[x], e.cap - e.flow);
Q.push(e.to);
}
}
if(a[t])
break;
}
if(!a[t])
break;
for(int u = t;u != s;u = edges[p[u]].from)
{
edges[p[u]].flow += a[t];
edges[p[u] ^1].flow -= a[t];
}
flow += a[t];
}
return flow;
}
}ek;
int in[maxn];
int main()
{
while(cin>>n>>m, n + m)
{
memset(in, 0, sizeof(in));
ek.init(n);
m--;
for(int i = 1;i <= n - 1;i++)
{
int a, b, c;
cin>>a>>b>>c;
a--;
b--;
in[a]++;
in[b]++;
ek.AddEdge(a, b, c);
ek.AddEdge(b, a, c);
}
for(int i = 0;i <= n - 1;i++)
{
if(i != m&&in[i] == 1)
{
ek.AddEdge(i, n, INF);
}
}
cout<<ek.MaxFlow(m, n)<<endl;
}
return 0;
}