POJ 1330 Nearest Common Ancestors 倍增算法的LCA

POJ 1330 Nearest Common Ancestors

题意：最近公共祖先的裸题

思路：LCA和ST我们已经很熟悉了，但是这里的f[i][j]却有相似却又不同的含义。f[i][j]表示i节点的第2^j个父亲是多少

　　 　　这个代码不是我的，转自 邝斌博客

 /* ***********************************************
 Author        :kuangbin
 Created Time  :2013-9-5 9:45:17
 File Name     :F:\2013ACM练习\专题学习\LCA\POJ1330_3.cpp
 ************************************************ */

 #include <stdio.h>
 #include <string.h>
 #include <iostream>
 #include <algorithm>
 #include <vector>
 #include <queue>
 #include <set>
 #include <map>
 #include <string>
 #include <math.h>
 #include <stdlib.h>
 #include <time.h>
 using namespace std;
 /*
 * POJ 1330
 * LCA 在线算法
 */
 const int MAXN = ;
 const int DEG = ;

 struct Edge
 {
     int to, next;
 }edge[MAXN * ];
 int head[MAXN], tot;
 void addedge(int u, int v)
 {
     edge[tot].to = v;
     edge[tot].next = head[u];
     head[u] = tot++;
 }
 void init()
 {
     tot = ;
     memset(head, -, sizeof(head));
 }
 int fa[MAXN][DEG];//fa[i][j]表示结点i的第2^j个祖先
 int deg[MAXN];//深度数组

 void BFS(int root)
 {
     queue<int>que;
     deg[root] = ;
     fa[root][] = root;
     que.push(root);
     while (!que.empty())
     {
         int tmp = que.front();
         que.pop();
         for (int i = ; i < DEG; i++)
             fa[tmp][i] = fa[fa[tmp][i - ]][i - ];
         for (int i = head[tmp]; i != -; i = edge[i].next)
         {
             int v = edge[i].to;
             if (v == fa[tmp][])continue;
             deg[v] = deg[tmp] + ;
             fa[v][] = tmp;
             que.push(v);
         }

     }
 }
 int LCA(int u, int v)
 {
     if (deg[u] > deg[v])swap(u, v);
     int hu = deg[u], hv = deg[v];
     int tu = u, tv = v;
     for (int det = hv - hu, i = ; det; det >>= , i++)
     if (det & )
         tv = fa[tv][i];
     if (tu == tv)return tu;
     for (int i = DEG - ; i >= ; i--)
     {
         if (fa[tu][i] == fa[tv][i])
             continue;
         tu = fa[tu][i];
         tv = fa[tv][i];
     }
     return fa[tu][];
 }
 bool flag[MAXN];
 int main()
 {
     freopen("in.txt","r",stdin);
     //freopen("out.txt","w",stdout);
     int T;
     int n;
     int u, v;
     scanf("%d", &T);
     while (T--)
     {
         scanf("%d", &n);
         init();
         memset(flag, false, sizeof(flag));
         for (int i = ; i < n; i++)
         {
             scanf("%d%d", &u, &v);
             addedge(u, v);
             addedge(v, u);
             flag[v] = true;
         }
         int root;
         for (int i = ; i <= n; i++)
         if (!flag[i])
         {
             root = i;
             break;
         }
         BFS(root);
         scanf("%d%d", &u, &v);
         printf("%d\n", LCA(u, v));
     }
     return ;
 }