Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path1->2->3which represents the number123.
Find the total sum of all root-to-leaf numbers.
Note: A leaf is a node with no children.
Example:
Input: [1,2,3]
1
/ \
2 3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
Example 2:
Input: [4,9,0,5,1]
4
/ \
9 0
/ \
5 1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
分析
叶子只负责算Pathsum。root只负责把左右相加。值得注意的做法
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def sumNumbers(self, root):
"""
:type root: TreeNode
:rtype: int
"""
return self.dfs(root,0)
def dfs(self,root,pathsum):
if not root:
return 0
#leaf get pathsum
if not root.left and not root.right:
return root.val+pathsum*10
#root only calculate
return self.dfs(root.left, pathsum*10+root.val)+self.dfs(root.right, pathsum*10+root.val)