sumofLeftLeaves.js

////////////////////////////////////////////////Sum of Left Leaves///////////////////////////////////////////
// Given the root of a binary tree, return the sum of all left leaves.
// Example 1:
// Input: root = [3,9,20,null,null,15,7]
// Output: 24
// Explanation: There are two left leaves in the binary tree, with values 9 and 15 respectively.
// Example 2:
//
// Input: root = [1]
// Output: 0
/**
 * 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}
 */
 const sumOfLeftLeaves = function(root) {
    const queue = [root];
    let sum = 0;

    while (queue.length > 0) {
        const current = queue.shift();

        if (current.left) {
            if (!current.left.left && !current.left.right) {
                sum += current.left.val;
            } else {
                queue.push(current.left);
            }
        }

        if (current.right) {
            queue.push(current.right);
        }
    }

    return sum;
};

// console.log(sumOfLeftLeaves([3,9,20,null,null,15,7]));
// console.log(sumOfLeftLeaves([1]));