Codeforces 219D. Choosing Capital for Treeland (树dp)

题目链接：http://codeforces.com/contest/219/problem/D

树dp

 //#pragma comment(linker, "/STACK:102400000, 102400000")
 #include <algorithm>
 #include <iostream>
 #include <cstdlib>
 #include <cstring>
 #include <cstdio>
 #include <vector>
 #include <cmath>
 #include <ctime>
 #include <list>
 #include <set>
 #include <map>
 using namespace std;
 typedef long long LL;
 typedef pair <int, int> P;
 const int N = 2e5 + ;
 struct Edge {
     int next, to, cost;
 }edge[N << ];
 int head[N], tot, d[N], ans1[N], ans[N];
 int res[N];

 inline void add_edge(int u, int v, int c) {
     edge[tot].next = head[u];
     edge[tot].to = v;
     edge[tot].cost = c;
     head[u] = tot++;
 }

 void dfs1(int u, int p) {
     d[u] = ;
     ans1[u] = ;
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(v == p)
             continue;
         dfs1(v, u);
         d[u] += d[v];
         ans1[u] += edge[i].cost + ans1[v];
     }
 }

 void dfs2(int u, int p) {
     ans[u] += ans1[u];
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(v == p)
             continue;
         ans[v] = ans[u] - ans1[v] - edge[i].cost + !edge[i].cost;
         dfs2(v, u);
     }
 }

 int main()
 {
     memset(head, -, sizeof(head));
     int n, u, v;
     scanf("%d", &n);
     for(int i = ; i < n; ++i) {
         scanf("%d %d", &u, &v);
         add_edge(u, v, );
         add_edge(v, u, );
     }
     dfs1(, -);
     dfs2(, -);
     int Min = N, cnt = ;
     for(int i = ; i <= n; ++i) {
         Min = min(Min, ans[i]);
     }
     for(int i = ; i <= n; ++i) {
         if(ans[i] == Min) {
             res[++cnt] = i;
         }
     }
     printf("%d\n", Min);
     sort(res + , res + cnt + );
     for(int i = ; i <= cnt; ++i) {
         printf("%d%c", res[i], i == cnt ? '\n': ' ');
     }
     return ;
 }