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235. Lowest Common Ancestor of a Binary Search Tree

时间:2017-10-30 11:25:42      阅读:150      评论:0      收藏:0      [点我收藏+]

标签:lca   tree   blog   and   public   class   code   esc   ini   

 

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        _______6______
       /                  ___2__          ___8__
   /      \        /         0      _4       7       9
         /           3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

 

思路:因为是bst, 如果root,的值介于pq之间,root就是共同祖先。

root不是共同祖先,则递归地判断左右子树是不是公共祖先。

 

递归版:

 

1 class Solution {
2     public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
3         if((root.val-p.val)*(root.val-q.val)<=0) return root;
4         return lowestCommonAncestor((root.val-p.val)>0?root.left:root.right, p, q);
5     }
6 }

 

 

循环版:

1 class Solution {
2     public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
3         while((root.val-p.val)*(root.val-q.val)>0)
4             root = ((root.val-p.val)>0?root.left:root.right);
5         return root;
6     
7     }
8 }

 

235. Lowest Common Ancestor of a Binary Search Tree

标签:lca   tree   blog   and   public   class   code   esc   ini   

原文地址:http://www.cnblogs.com/zle1992/p/7753161.html

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