Day-26_Sum_root_to_Leaf_numbers.py

'''
	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.

'''

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumNumbers(self, root: TreeNode) -> int:
        if root is None:
            return 0
        total = 0
        stack = [(0, root)]
        while len(stack) > 0:
            new_stack = []
            for value, node in stack:
                node_total = value * 10 + node.val
                if node.left is None and node.right is None:
                    total += node_total
                if node.left is not None:
                    new_stack.append((node_total, node.left))
                if node.right is not None:
                    new_stack.append((node_total, node.right))
            stack = new_stack
        return total