和poj 1655差不多，那道会了这个也就差不多了。
题意:从小到大输出树的重心。
题会卡stl，要用邻接表存树。。。。。
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 using namespace std; 6 const int maxn = 50006; 7 const int INF = 1 << 30; 8 int head[maxn]; 9 int son[maxn], ans[maxn]; 10 bool vis[maxn]; 11 int n, siz, cnt, tot; 12 struct Edge 13 { 14 int to, next; 15 }; 16 Edge edge[maxn * 2]; 17 18 void Init() 19 { 20 memset(vis, 0, sizeof(vis)); 21 memset(head, -1, sizeof(head)); 22 siz = INF; 23 cnt = tot = 0; 24 } 25 26 27 void add(int u, int v) 28 { 29 edge[cnt].to = v; 30 edge[cnt].next = head[u]; 31 head[u] = cnt++; 32 } 33 34 void dfs(int u) 35 { 36 vis[u] = 1; 37 son[u] = 1; 38 int tmp = 0; 39 for (int i = head[u]; i != -1; i = edge[i].next) 40 { 41 int v = edge[i].to; 42 if (!vis[v]) { 43 dfs(v); 44 son[u] += son[v]; 45 tmp = max(tmp, son[v]); 46 } 47 } 48 tmp = max(tmp, n - son[u]); 49 if (tmp == siz) { 50 ans[tot++] = u; 51 } 52 else if (tmp<siz) { 53 tot = 0; 54 ans[tot++] = u; 55 siz = tmp; 56 } 57 } 58 59 int main() 60 { 61 while (scanf("%d", &n) == 1) 62 { 63 Init(); 64 for (int i = 1; i < n; i++) { 65 int u, v; 66 scanf("%d%d", &u, &v); 67 add(u, v); 68 add(v, u); 69 } 70 dfs(1); 71 sort(ans, ans + tot); 72 for (int i = 0; i<tot; i++) { 73 printf("%d ", ans[i]); 74 } 75 printf(" "); 76 } 77 return 0; 78 }