leetcode oj Sum of Left Leaves

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一、问题描述：

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

Example:

    3/ \9  20/  \15   7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

二、思路：

      先序遍历二叉树，判断结点是否为左叶子结点：

三、实现代码：

public class Solution {public int sumOfLeftLeaves(TreeNode root) {if (root== null) {return 0;}if (root.left != null && root.left.right == null && root.left.left == null) {return root.left.val + sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);}return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);}
}

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