leetcode做题记录 —— sum-of-left-leaves

sum-of-left-leaves 
Find the sum of all left leaves in a given binary tree.

Example:

1.         3    
2.        /  \   
3.       9    20
4.           /  \   
5.           15   7 

There are two left leaves in the binary tree, with values 9 and 15 
respectively. Return 24.

sum-of-left-leaves

给定一个二叉树，求所有左叶子节点的和。

解法

这题比较简单，做个递归把左叶子节点的的值加起来就可以了。

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

End