[leetcode] 1302. Deepest Leaves Sum

Description

Given a binary tree, return the sum of values of its deepest leaves.

Example 1:

Input: root = [1,2,3,4,5,null,6,7,null,null,null,null,8]
Output: 15

Constraints:

• The number of nodes in the tree is between 1 and 10^4.
• The value of nodes is between 1 and 100.

分析

题目的意思是：求出二叉树最深的叶子结点的和，我的办法挺笨的，首先递归找到最大深度，然后再遍历求出最大深度的叶子结点。我看了另一种思路是用一个全局变量来存储最大深度d，用sum存储叶子结点的和，当当前的深度depth>d时，更新d，然后sum置0.当depth==d时，sum要加上当前的值，然后进行递归，思路比我好，哈哈。

代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def getDepth(self,root,depth):
        if(root is None):
            return 
        self.getDepth(root.left,depth+1)
        self.getDepth(root.right,depth+1)
        self.maxDepth=max(self.maxDepth,depth)
        
    def solve(self,root,depth):
        if(root is None):
            return 0
        l=self.solve(root.left,depth+1)
        r=self.solve(root.right,depth+1)
        if(root.left is None and root.right is None and depth==self.maxDepth):
            return root.val
        return l+r
        
    def deepestLeavesSum(self, root: TreeNode) -> int:
        self.maxDepth=0
        self.getDepth(root,0)
        res=self.solve(root,0)
        return res

参考文献

​​[LeetCode] [Java] Recursive, faster than 100.00%​​