PathSum.js

// Source : https://leetcode.com/problems/path-sum
// Author : Dean Shi
// Date   : 2021-12-14

/***************************************************************************************
 * Given the root of a binary tree and an integer targetSum, return true if the tree
 * has a root-to-leaf path such that adding up all the values along the path equals
 * targetSum.
 * 
 * A leaf is a node with no children.
 * 
 * Example 1:
 * 
 * Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
 * Output: true
 * Explanation: The root-to-leaf path with the target sum is shown.
 * 
 * Example 2:
 * 
 * Input: root = [1,2,3], targetSum = 5
 * Output: false
 * Explanation: There two root-to-leaf paths in the tree:
 * (1 --> 2): The sum is 3.
 * (1 --> 3): The sum is 4.
 * There is no root-to-leaf path with sum = 5.
 * 
 * Example 3:
 * 
 * Input: root = [], targetSum = 0
 * Output: false
 * Explanation: Since the tree is empty, there are no root-to-leaf paths.
 * 
 * Constraints:
 * 
 * The number of nodes in the tree is in the range [0, 5000].
 * -1000 <= Node.val <= 1000
 * -1000 <= targetSum <= 1000
 * 
 * 
 ***************************************************************************************/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} sum
 * @return {boolean}
 */
var hasPathSum = function(root, sum) {
    if (!root) {
        return false;
    }
    const targetSum = sum - root.val
    if (targetSum === 0 && !root.left && !root.right) {
        return true
    }
    return hasPathSum(root.left, targetSum) || hasPathSum(root.right, targetSum)
};