#Leetcode# 235. Lowest Common Ancestor of a Binary Search Tr

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

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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 p and q?as the lowest node in T that has both p and q?as descendants (where we allow?a node to be a descendant of itself).”

Given binary search tree:? root =?[6,2,8,4,7,9,null,3,5]

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Example 1:

Input: root = [6,5],p = 2,q = 8
Output: 6
Explanation: The LCA of nodes  and  is .
286

Example 2:

Input: root = [6,q = 4
Output: 2
Explanation: The LCA of nodes  and  is,since a node can be a descendant of itself according to the LCA definition.
242

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Note:

• All of the nodes‘ values will be unique.
• p and q are different and both values will?exist in the BST.

代码：

/**
 * 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) {
        int v1 = p -> val;
        int v2 = q -> val;
        int r = root -> val;
        if(v1 > r && v2 < r || v1 < r && v2 > r)
            return root;
        if(v1 == r || v2 == r)
            return root;
        if(v1 < r)
            return lowestCommonAncestor(root -> left,p,q);
        else
            return lowestCommonAncestor(root -> right,q);
    }
};

　　感觉好多递归哦