Leetcode•Jul 03, 2025
Lowest Common Ancestor of a Binary Search Tree
Hazrat Ali
Leetcode
According to 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
Solution
/**
* @param {TreeNode} root
* @param {TreeNode} p
* @param {TreeNode} q
* @return {TreeNode}
*/
const lowestCommonAncestor = (root, p, q) => {
if (!root) {
return null;
}
if (root.val > p.val && root.val > q.val) {
return lowestCommonAncestor(root.left, p, q);
}
if (root.val < p.val && root.val < q.val) {
return lowestCommonAncestor(root.right, p, q);
}
return root;
};