Sum Root to Leaf Numbers

题目描述

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

解题方法

DFS

和path sum一样的解法，只不过这里记录的是value组成的string, 当遇到leaf的时候再转换成Int加到结果里

Solution

# 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
        """
        if not root:
            return 0

        stack = []
        result = 0
        stack.append((root, str(root.val)))
        while stack:
            curNode, curSum = stack.pop()
            if not curNode.left and not curNode.right:
                result += int(curSum)
            if curNode.left:
                stack.append((curNode.left, curSum + str(curNode.left.val)))
            if curNode.right:
                stack.append((curNode.right, curSum + str(curNode.right.val)))
        return result

Reference