LeetCode404_404. The sum of the left leaves

LeetCode404_404. The sum of the left leaves

1. Description

Given the root node root of a binary tree, return the sum of all left leaves.

Example 1:

输入: root = [3,9,20,null,null,15,7] 
输出: 24 
解释: 在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24

Example 2:

输入: root = [1]
输出: 0

hint:

The number of nodes is in the range [1, 1000]
-1000 <= Node.val <= 1000

Two, solution

Method 1: Recursion

    //AC Your runtime beats 99.90 % of java submissions.
    //102 / 102 test cases passed.	Status: Accepted	Runtime: 8 ms
    public int sumOfLeftLeaves(TreeNode root) {
    
    
        if (root == null) return 0;
        if (root.left != null && root.left.left == null && root.left.right == null)
            return root.left.val + sumOfLeftLeaves(root.right);
        return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
    }

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