POJ 3107 Godfather (树重心)

题目链接：http://poj.org/problem?id=3107

题意:

数重心，并按从小到大输出。

思路:

dfs

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <vector>
 using namespace std;
 const int N = 5e4 + ;
 struct Edge {
     int next, to;
 }edge[N << ];
 vector <int> G[N];
 int dp[N], n, head[N], cnt;

 inline void add(int u, int v) {
     edge[cnt].next = head[u];
     edge[cnt].to = v;
     head[u] = cnt++;
 }

 int dfs(int u, int p) {
     dp[u] = ;
     int sum = ;
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(v == p)
             continue;
         int temp = dfs(v, u);
         dp[u] = max(dp[u], temp);
         sum += temp;
     }
     dp[u] = max(dp[u], n - sum - );
     return sum + ;
 }

 int main()
 {
     while(~scanf("%d", &n)) {
         for(int i = ; i <= n; ++i) {
             head[i] = -;
         }
         cnt = ;
         for(int i = ; i < n; ++i) {
             int u, v;
             scanf("%d %d", &u, &v);
             add(u, v);
             add(v, u);
         }
         dfs(, -);
         int Max = n;
         vector <int> ans;
         for(int i = ; i <= n; ++i) {
             Max = min(Max, dp[i]);
         }
         for(int i = ; i <= n; ++i) {
             if(Max == dp[i]) {
                 ans.push_back(i);
             }
         }
         for(int i = ; i < ans.size(); ++i) {
             if(i == ans.size() - ) {
                 printf("%d\n", ans[i]);
             } else {
                 printf("%d ", ans[i]);
             }
         }
     }
     return ;
 }