UVa 1218 Perfect Service [DFS+DP]

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <cstdlib>
#include <algorithm>
using namespace std;

const int maxn = 10240, inf = (1<<27);
int n, vis[maxn], dp[maxn][3];
vector<int> G[maxn], sons[maxn];

void DFS(const int u){
for (unsigned i = 0; i != G[u].size(); ++i) if(!vis[G[u][i]]) {
sons[u].push_back(G[u][i]);
vis[G[u][i]] = true;
DFS(G[u][i]);
}
}
int solve(const int u, const int k){
if (dp[u][k] != -1) return dp[u][k];
int & ans = dp[u][k];
if (k == 0) ans = 1; if (k == 1) ans = 0; if (k == 2) ans = inf;
for (unsigned i = 0; i != sons[u].size(); ++i){
int v = sons[u][i];
if (k == 0) ans += min(solve(v, 0), solve(v, 1));
if (k == 1) ans += solve(v, 2);
if (k == 2) ans = min(ans, solve(u, 1) - solve(v, 2) + solve(v, 0));
if (ans > inf) ans = inf;
}
return ans;
}

int main(){
//freopen("in.txt", "r", stdin);
while (cin >> n){
memset(G, 0, sizeof(G)); memset(sons, 0, sizeof(sons));
memset(vis, 0, sizeof(vis)); memset(dp, -1, sizeof(dp));
for (int i = 1; i < n; ++i){
int x, y; cin >> x >> y;
G[x].push_back(y); G[y].push_back(x);
}
vis[1] = true; DFS(1);
cout << min(solve(1, 0), solve(1, 2)) << endl;
cin >> n; if (n == -1) return 0;
}
return 0;
}