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| /*
*File: 1848.cpp
*Date : 2015-05-21 22:28:22
*/
#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
typedef long long LL;
#define clr(x) memset((x),0,sizeof(x))
#define inf 0x3f3f3f3f
using namespace std;
LL dp[110][3];
vector <int> v[110];
int n;
LL dfs(int x,int l,int fa)
{
if(dp[x][l]!=-1) return dp[x][l];
LL ans = inf;
int t = v[x].size();
if(t == 1&&v[x][0] == fa)
{
if(l ==2)
return dp[x][l] = 0;
else return dp[x][l] = inf;
}
if(l == 1)
{
int len = v[x].size();
LL tmp = 0;
for(int i = 0 ;i<len;i++) if(v[x][i]!=fa)
{
tmp = dfs(v[x][i],0,x);
for(int j = 0;j<len;j++) if(j!=i&&v[x][j]!=fa)
{
tmp += dfs(v[x][j],1,x);
}
}
ans = min(ans,tmp+1);
for(int i =0;i<len;i++) if(v[x][i]!=fa)
{
for(int j = 0;j<len;j++) if(i!=j&&v[x][j]!=fa)
{
LL tmp = 0;
for(int t = 0;t<len;t++) if(t!=i&&t!=j&&v[x][t]!=fa)
{
tmp += dfs(v[x][t],1,x);
}
ans = min(ans,tmp+dfs(v[x][i],0,x)+dfs(v[x][j],0,x)+1);
ans = min(ans,tmp+dfs(v[x][i],2,x)+dfs(v[x][j],0,x)+1);
ans = min(ans,tmp+dfs(v[x][i],2,x)+dfs(v[x][j],2,x)+1);
}
}
// printf("%d %d %d\n",x,l,ans);
return dp[x][l] = ans;
}
else if(l == 0)
{
LL tt;
for(int i = 0;i<v[x].size();i++) if(v[x][i]!=fa)
{
tt = min(dfs(v[x][i],0,x),dfs(v[x][i],2,x));
for(int j = 0;j<v[x].size();j++) if(i!=j&&v[x][j]!=fa)
{
tt+= dfs(v[x][j],1,x);
}
ans = min(ans,tt);
}
// printf("%d %d %d\n",x,l,ans);
return dp[x][l] = ans;
}
else if(l==2)
{
LL tmp = 0;
for(int i =0;i<v[x].size();i++) if(v[x][i]!=fa)
{
tmp += dfs(v[x][i],1,x);
}
ans = min(ans,tmp);
// printf("%d %d %d\n",x,l,ans);
return dp[x][l] =ans;
}
}
int main()
{
while(~scanf("%d",&n))
{
int x,y;
memset(dp,-1,sizeof dp);
for(int i= 1;i<=n;i++)
v[i].clear();
for(int i = 1;i<n;i++)
{
scanf("%d%d",&x,&y);
v[x].push_back(y);
v[y].push_back(x);
}
LL ans = dfs(1,1,0) ;
if(ans >= inf)
ans = -1;
printf("%lld\n", ans);
}
return 0;
}
|