LeetCode //C - 235. Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node 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)."

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.

Example 3:

Input: root = [2,1], p = 2, q = 1
Output: 2

Constraints:
  • The number of nodes in the tree is in the range [ 2 , 1 0 5 ] [2, 10^5] [2,105].
  • − 1 0 9 < = N o d e . v a l < = 1 0 9 -10^9 <= Node.val <= 10^9 −109<=Node.val<=109
  • All Node.val are unique.
  • p != q
  • p and q will exist in the BST.

From: LeetCode

Link: 233. Number of Digit One


Solution:

Ideas:
  • Start from the root and keep traversing the tree.
  • Depending on the values of p and q relative to the current node, move left or right.
  • If you find a node where p and q lie on different sides (or one of them is equal to the current node), that node is the LCA.
Code:
c 复制代码
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q) {
    while (root != NULL) {
        // If both p and q are greater than root, LCA lies in the right subtree
        if (p->val > root->val && q->val > root->val) {
            root = root->right;
        }
        // If both p and q are smaller than root, LCA lies in the left subtree
        else if (p->val < root->val && q->val < root->val) {
            root = root->left;
        }
        // We have found the split point, i.e. the LCA node
        else {
            return root;
        }
    }
    return NULL; // this line will never be reached if p and q are guaranteed to be in the tree
}
相关推荐
聚客AI16 小时前
🙋‍♀️Transformer训练与推理全流程:从输入处理到输出生成
人工智能·算法·llm
大怪v19 小时前
前端:人工智能?我也会啊!来个花活,😎😎😎“自动驾驶”整起!
前端·javascript·算法
惯导马工20 小时前
【论文导读】ORB-SLAM3:An Accurate Open-Source Library for Visual, Visual-Inertial and
深度学习·算法
骑自行车的码农1 天前
【React用到的一些算法】游标和栈
算法·react.js
博笙困了1 天前
AcWing学习——双指针算法
c++·算法
moonlifesudo1 天前
322:零钱兑换(三种方法)
算法
NAGNIP2 天前
大模型框架性能优化策略:延迟、吞吐量与成本权衡
算法
美团技术团队2 天前
LongCat-Flash:如何使用 SGLang 部署美团 Agentic 模型
人工智能·算法
Fanxt_Ja2 天前
【LeetCode】算法详解#15 ---环形链表II
数据结构·算法·leetcode·链表
侃侃_天下2 天前
最终的信号类
开发语言·c++·算法