首发于 语雀@blueju

    https://leetcode-cn.com/problems/sum-of-left-leaves/

    1. /**
    2.  * Definition for a binary tree node.
    3.  * function TreeNode(val, left, right) {
    4.  *     this.val = (val===undefined ? 0 : val)
    5.  *     this.left = (left===undefined ? null : left)
    6.  *     this.right = (right===undefined ? null : right)
    7.  * }
    8.  */
    9. /**
    10.  * @param {TreeNode} root
    11.  * @return {number}
    12.  */
    13. var sumOfLeftLeaves = function (root) {
    14.     let sum = 0
    15.     function traverse(root) {
    16.         if (root === null) {
    17.             return
    18.         }
    19.         if (root.left !== null) {
    20.             if (root.left.left === null && root.left.right === null) {
    21.                 sum = sum + root.left.val
    22.             } else {
    23.                 traverse(root.left)
    24.             }
    25.         }
    26.         root.right && traverse(root.right)
    27.     }
    28.     traverse(root)
    29.     return sum
    30. };