Sum Root-to-Leaf Numbers

Given a binary tree, find the sum of all the numbers, that are formed by the digits from root to leaf paths.

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Note: Each node of the tree represents a single digit number i.e. (0-9). Root node denotes the most significant digit of any number formed.

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Example:

Input :
      1                                  
     / \                                   
    2   3

Output :
    12 + 13 = 25