【CF】135 Div2 Choosing Capital for Treeland

树形结构，挺有意思的题目。不难。

 /* 219D */
 #include <iostream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 #include <iterator>
 #include <iomanip>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const int maxn = 2e5+;
 int D[maxn];
 int W[maxn], sw;
 int W_[maxn];
 vpii E[maxn];
 vi vc;
 int ans;
 int n;

 void dfs(int u, int fa, int w_, int d) {
     int v, w;

     D[u] = d;
     W_[u] = w_;
     rep(i, , SZ(E[u])) {
         v = E[u][i].fir;
         w = E[u][i].sec;
         if (v == fa)
             continue;
         dfs(v, u, w_+w, d+);
         W[u] += W[v] + w;
     }
 }

 void solve() {
     // calculate w & c
     dfs(, -, , );
     ans = sw = W[];
     vc.pb();

     // calculate the minimum cost
     int tmp;

     rep(i, , n+) {
         tmp = sw - W_[i] + D[i] - W_[i];
         if (tmp == ans) {
             vc.pb(i);
         } else if (tmp < ans) {
             vc.clear();
             ans = tmp;
             vc.pb(i);
         }
     }

     printf("%d\n", ans);
     rep(i, , SZ(vc))
         printf("%d ", vc[i]);
     putchar('\n');
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     int u, v;

     scanf("%d", &n);
     rep(i, , n) {
         scanf("%d %d", &u, &v);
         E[u].pb(mp(v, ));
         E[v].pb(mp(u, ));
     }

     solve();

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }