【leetcode】【91.6】【M】Sum Root to Leaf Numbers

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.

For example,

1

/ \

2 3

The root-to-leaf path

1->2

represents
the number

12

.

The root-to-leaf path

1->3

represents
the number

13

.

Return the sum = 12 + 13 =

25

.

还是得用递归做

开始的时候总是出问题，关键就在于，如果输入是12345的时候，13对应的是13，而不是130

也就是说不能按照每一层来算，因为同样是1，在124这条路径上，1表示一百，在13这条路径上，表示的是10

关键点就在于，什么时候把当前结果加到总的结果上——应该是到叶子节点的时候，再一起加上去。用summ表示当前这条路径上的当前结果。只有这样，才能通过参数传进去。

# 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 __init__(self):

self.res = 0

def dfs(self,root,summ):

if root == None:

return

summ = root.val + summ*10

if root.left:

self.dfs(root.left,summ)

if root.right:

self.dfs(root.right,summ)

if root.left == None and root.right == None:

self.res += summ

#print root.val,summ

def sumNumbers(self, root):

self.dfs(root,0)

#print self.res

return self.res

"""

:type root: TreeNode

:rtype: int

"""