Sum of Left Leaves - LeetCode

sum-of-left-leaves.js

// https://leetcode.com/problems/sum-of-left-leaves/
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */

var isLeafNode = function(node) {
    if (!node) {
        return false;
    }
    if (node.left || node.right) {
        return false;
    }
    return true;
}

var sumOfLeftLeaves = function(root) {
    let sum = 0;
    if (root) {
        if (isLeafNode(root.left)) { // leaf node
            sum += root.left.val;
        } else {
            sum += sumOfLeftLeaves(root.left);
        }
        sum += sumOfLeftLeaves(root.right);
    }
    return sum;
};