LeetCode 0235 - Lowest Common Ancestor of a Binary Search Tree

Reck Zhang

发布于 2021-08-11 12:05:01

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发布于 2021-08-11 12:05:01

文章被收录于专栏：Reck Zhang

Lowest Common Ancestor of a Binary Search Tree

Desicription

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 = [6,2,8,0,4,7,9,null,null,3,5]

     _______6______
    /              \
 ___2__          ___8__
/      \        /      \
0      _4       7       9
      /  \
      3   5

Example 1:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
Explanation: The LCA of nodes 2 and 8 is 6.

Example 2:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself 
             according to the LCA definition.

Note:

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

Solution

/**
 * 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) {
        while((root->val - p->val) * (root->val - q->val) > 0) {
            root = root->val > p->val ? root->left : root->right;
        }
        return root;
    }
};

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原始发表：2018-09-13，如有侵权请联系 cloudcommunity@tencent.com 删除

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