算法之寻找二叉树结点的最近公共祖先

给定一个二叉树, 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，给定如下二叉树:  root = [3,5,1,6,2,0,8,null,null,7,4]

示例 1:
输入: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1输出: 3解释: 节点 5 和节点 1 的最近公共祖先是节点 3。
-----3--------5--- -1----6--2- 0--8----7-4

/** * 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 find(root, p, q);    }
    private TreeNode find(TreeNode node, TreeNode p, TreeNode q) {        if(node == null || node == p || node == q) {            return node;        }
        TreeNode left = find(node.left, p, q);        TreeNode right = find(node.right, p, q);
        if(left == null) return right;        if(right == null) return left;        return node;    }}

class Solution {		//记忆节点    TreeNode findNode = new TreeNode(0);    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        TreeNode node = find(root, p, q);        if(findNode.left == null || findNode.right == null) {            return null;        }        return node;    }
    private TreeNode find(TreeNode node, TreeNode p, TreeNode q) {        if(node == null) {            return node;        }        if(node == p) {            findNode.left = node;            return node;        }  else if(node == q) {            findNode.right = node;            return node;        }
        TreeNode left = find(node.left, p, q);        TreeNode right = find(node.right, p, q);
        if(left == null) return right;        if(right == null) return left;        return node;    }}