POJ 1470 Closest Common Ancestors LCA
http://poj.org/problem?id=1470
一个讲lca和rmq的文章，网上也可以搜到翻译：
http://www.topcoder.com/tc?d1=tutorials&d2=lowestCommonAncestor&module=Static
题意：给一棵树，询问多组lca，然后问各点作为lca被询问到的次数。
分析：第一次写倍增，很丑= =。。
1 #include<cstdio> 2 #include<cstring> 3 #include<algorithm> 4 #include<vector> 5 using namespace std; 6 7 int n, root; 8 int f[1000], lv[1000], p[1000][12], ans[1000]; 9 vector<int> son[900]; 10 int in() 11 { 12 int ret = 0; 13 char ch = getchar(); 14 while(!(ch >= '0' && ch <= '9')) ch = getchar(); 15 while(ch >= '0' && ch <= '9'){ 16 ret = ret * 10 + ch - '0'; 17 ch = getchar(); 18 } 19 return ret; 20 } 21 void dfs(int x, int dep) 22 { 23 lv[x] = dep; 24 for (int i = 0; i < son[x].size(); i ++) 25 dfs(son[x][i], dep+1); 26 } 27 void work() 28 { 29 memset(p, 0, sizeof(p)); 30 for (int i = 0; i <= n; i++) 31 p[i][0] = f[i]; 32 for (int j = 1; (1 << j) <= n; j++){ 33 for (int i = 1; i <= n; i++){ 34 int tmp = p[i][j-1]; 35 p[i][j] = p[tmp][j-1]; 36 } 37 } 38 } 39 int lca(int x, int y) 40 { 41 if (lv[x] < lv[y]) swap(x, y); 42 int log; 43 for (log = 1; (1 << log) <= lv[x]; log++); 44 log --; 45 for (int i = log; i >= 0; i--){ 46 //if (lv[x] - (1 << i) >= lv[y]) x = p[x][i]; 47 int tmp = p[x][i]; 48 if (tmp != 0 && lv[tmp] >= lv[y]) x = p[x][i]; 49 } 50 if (x == y) return x; 51 for (int i = log; i >= 0; i--){ 52 if (p[x][i] != p[y][i] && p[x][i] != 0) x = p[x][i], y = p[y][i]; 53 } 54 return f[x]; 55 } 56 int main() 57 { 58 while(scanf("%d", &n) != EOF) 59 { 60 memset(f, 0, sizeof(f)); 61 int x, y, z; 62 for (int i = 0; i < n; i++){ 63 x = in(); y = in(); 64 son[x].clear(); 65 for (int j = 1; j <= y; j++){ 66 z = in(); 67 f[z] = x; 68 son[x].push_back(z); 69 } 70 } 71 for (int i = 1; i <= n; i++) 72 if (f[i] == 0) root = i, f[root] = root; 73 dfs(root, 1); 74 work(); 75 int q; 76 q = in(); 77 memset(ans, 0, sizeof(ans)); 78 for (int i = 0; i < q; i++){ 79 x = in(); y = in(); 80 ans[lca(x, y)] ++; 81 } 82 for (int i = 1; i <= n; i++) if (ans[i]) 83 printf("%d:%d\n", i, ans[i]); 84 } 85 return 0; 86 }
