剑指 Offer 68 - I. 二叉树（搜索树）的最近公共祖先

给定一个二叉搜索树, 找到该树中两个指定节点的最近公共祖先。

百度百科中最近公共祖先的定义为：“对于有根树 T 的两个结点 p、q，最近公共祖先表示为一个结点 x，满足 x 是 p、q 的祖先且 x 的深度尽可能大（一个节点也可以是它自己的祖先）。”

例如，给定如下二叉搜索树: root = [6,2,8,0,4,7,9,null,null,3,5]

java

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { return recurr( root, p, q); } TreeNode recurr(TreeNode root, TreeNode p, TreeNode q){ while(root!=null){ if(root.val<p.val && root.val<q.val) root = root.right; else if(root.val>p.val&& root.val>q.val) root = root.left; else break; } return root; } }

二叉树的最近公共祖先

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(root==p|| root==q || root==null) return root; TreeNode left = lowestCommonAncestor(root.left,p,q); TreeNode right = lowestCommonAncestor(root.right,p,q); if(left==null && right==null) return null; if(left==null) return right; if(right==null) return left; return root; } }