LeetCode 235. Lowest Common Ancestor of a Binary Search Tree（BST求最近公共祖先）

题意：求BST中两点的最近公共祖先。

/**
 * 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 == NULL) return NULL;
        if(p -> val < root -> val && q -> val < root -> val) return lowestCommonAncestor(root -> left, p, q);
        if(p -> val > root -> val && q -> val > root -> val) return lowestCommonAncestor(root -> right, p, q);
        return root;
    }
};