Leetcode
2020.05.01 18:51
235. Lowest Common Ancestor of a Binary Search Tree
조회 수 894 추천 수 0 댓글 0
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]

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 nodes2
and8
is6
.
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 nodes2
and4
is2
, 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.
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { TreeNode pNode = p; TreeNode qNode = q; TreeNode node = root; while(node != null){ TreeNode parent = node; if(parent.val < qNode.val && parent.val < pNode.val){ node = node.right; }else if(qNode.val < parent.val && pNode.val < parent.val){ node = node.left; }else{ return node; } } return null; } }
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { TreeNode pNode = p; TreeNode qNode = q; if(root.val < qNode.val && root.val < pNode.val){ return lowestCommonAncestor(root.right, p, q); }else if(qNode.val < root.val && pNode.val < root.val){ return lowestCommonAncestor(root.left, p, q); } return root; } }
[문제] https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/