POJ1655 Balancing Act(树的重心)

题目链接 Balancing Act

就是求一棵树的重心，然后统计答案。

 1 #include <bits/stdc++.h>
 2
 3 using namespace std;
 4
 5 #define REP(i,n)                for(int i(0); i <  (n); ++i)
 6 #define for_edge(i,x)           for(int i = H[x]; i; i = X[i])
 7
 8 const int INF = 1 << 30;
 9 const int N     =    100000      +       10;
10
11 int H[N << 1], E[N << 1], X[N << 1];
12 int T, et, n, x, y;
13 int son[N];
14 int ans_size, ans;
15
16 inline void addedge(int a, int b){
17     E[++et] = b, X[et] = H[a], H[a] = et;
18     E[++et] = a, X[et] = H[b], H[b] = et;
19 }
20
21 void dfs(int x, int fa){
22     int sn = 0;
23     for_edge(i, x){
24         int u = E[i];
25         if (u != fa){
26             dfs(u, x);
27             son[x] += son[u];
28             sn = max(sn, son[u]);
29         }
30     }
31     ++son[x];
32     sn = max(sn, n - son[x]);
33     if (ans_size > sn || ans_size == sn && ans > x){
34         ans_size = sn;
35         ans = x;
36     }
37
38 }
39
40 int main(){
41
42     scanf("%d", &T);
43     for (; T--;){
44         ans_size = INF; ans = INF;
45         memset(H, 0, sizeof H);
46         memset(son, 0, sizeof son);
47         et = 0;
48         scanf("%d", &n);
49         REP(i, n - 1){
50             scanf("%d%d", &x, &y);
51             addedge(x, y);
52         }
53         dfs(1, 0);
54         printf("%d %d\n", ans, ans_size);
55     }
56
57     return 0;
58
59 }