Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path 1->2->3 which represents the number 123.
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.
Solutions
1. DFS-递归
先序遍历即可。
# Time Complexity: O(n)
# Space Complexity: O(1)
# 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: TreeNode) -> int:
if not root:
return 0
res = [0]
self.dfs(root, '', res)
return res[0]
def dfs(self, root, strs, res):
if not root:
return
new_strs = strs+str(root.val)
if not root.left and not root.right:
res[0] += int(new_strs)
self.dfs(root.left, new_strs, res)
self.dfs(root.right, new_strs, res)
# Runtime: 28 ms, faster than 99.62% of Python3 online submissions for Sum Root to Leaf Numbers.
# Memory Usage: 12.9 MB, less than 100.00% of Python3 online submissions for Sum Root to Leaf Numbers.