2021.2.21 刷题（二叉搜索树的最近公共祖先）

题目链接：https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/
题目描述：

题解：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root->val > p->val && root->val > q->val)  //当前遍历的节点比p,q的值都大，祖先在当前节点的左子树
        {
            TreeNode *left = lowestCommonAncestor(root->left, p, q);
            if(left != NULL)
                return left;
        }
            
        if(root->val < p->val && root->val < q->val)    //当前遍历的节点比p,q的值都小，祖先在当前节点的右子树
        {
            TreeNode *right = lowestCommonAncestor(root->right, p, q);
            if(right != NULL)
                return right;
        }
        return root;
    }
};