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404. 左叶子之和

English Version

题目描述

计算给定二叉树的所有左叶子之和。

示例：

    3
   / \
  9  20
    /  \
   15   7

在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24

 

解法

Python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def sumOfLeftLeaves(self, root: TreeNode) -> int:
        if root is None:
            return 0
        res = 0
        if root.left and root.left.left is None and root.left.right is None:
            res += root.left.val
        res += self.sumOfLeftLeaves(root.left)
        res += self.sumOfLeftLeaves(root.right)
        return res

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int res = 0;
        if (root.left != null && root.left.left == null && root.left.right == null) {
            res += root.left.val;
        }
        res += sumOfLeftLeaves(root.left);
        res += sumOfLeftLeaves(root.right);
        return res;
    }
}

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