leetcode129 -- Sum Root to Leaf Numbers

# 小郑之家~

### 题目

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.



### 解答

# 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:
res = []
if not root:
return 0
self.helper(root, res, [])
print(res)
summ = 0
for x in res:
for i in range(len(x)):
summ += x[i]*(10**(len(x)-1-i))

return summ

def helper(self, root, res, out):
if not root:
return
out.append(root.val)
if not root.left and not root.right:
res.append(out[:])
self.helper(root.left, res, out[:])
self.helper(root.right, res, out[:])



### 详细解的如下


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

class Solution(object):
def sumNumbers(self, root):
"""
:type root: TreeNode
:rtype: int
"""

res = []  # 用来放最终所有的从root到leaf的path

if not root:
return 0
self.helper(root, res, [])
summ = 0
for x in res:
# 算是几位数
for i in range(len(x)):
summ += x[i]*(10**(len(x)-1-i))
return summ

def helper(self, root, res, out):
"""
res 是用来放最终的结果，out是为了不断地来得到一个新的从根节点到叶子节点的path

"""
if not root:
return

out.append(root.val)

# 判断root,是否已经到leaft

if not root.left and not root.right:
res.append(out[:])

# 递归的去走左边和右边

self.helper(root.left, res, out[:])
self.helper(root.right, res, out[:])