题目介绍

力扣404题：leetcode-cn.com/problems/su…

分析

利用递归，代码简单演示如下：

class Solution {
    int sum = 0;
    public int sumOfLeftLeaves(TreeNode root) {
        leftSum(root);
        return sum;
    }

     public void leftSum(TreeNode root) {
         if(root == null) {
             return;
         }

         if(root.left != null && root.left.left == null && root.left.right == null) {
             sum += root.left.val;
         }
         leftSum(root.left);
         leftSum(root.right);
     }
}