July 6th 2023

Problem Description permalink

You are given the root of a binary search tree (BST) and an integer val.

Find the node in the BST that the node's value equals val and return the subtree rooted with that node. If such a node does not exist, return null.

Solution permalink

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function searchBST(root: TreeNode | null, val: number): TreeNode | null {
    if (root == null){
        return null;
    }

    if (root.val == val){
        return root;
    }

    const left = searchBST(root.left, val);
    if (left !== null){
        return left;
    }

    const right = searchBST(root.right, val);
    if (right !== null){
        return right;
    }

    return null;
};

Discussion permalink

This is a depth-first search that will always search all the way down the tree on the left side, then the right side.