Sum of Root To Leaf Binary Numbers — LeetCode 1022 Python Solution

The problem

You are given the root of a binary tree where each node has a value 0 or 1. Each root-to-leaf path represents a binary number starting with the most significant bit.

Example

Input

root = [1,0,1,0,1,0,1]

Output

22

Explanation

(100) + (101) + (110) + (111) = 4 + 5 + 6 + 7 = 22

Python solution

# 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 sumRootToLeaf(self, root: TreeNode) -> int:
        def dfs(root, t):
            if root is None:
                return 0
            t = (t << 1) | root.val
            if root.left is None and root.right is None:
                return t
            return dfs(root.left, t) + dfs(root.right, t)

        return dfs(root, 0)

Complexity

Pattern: Tree Traversal

Choose the order — preorder, inorder, postorder, level — and the problem solves itself. LeetCode 1022. Sum of Root To Leaf Binary Numbers is filed here because LeetCode tags it Tree and Binary Tree, which is the vocabulary this hub collects.

The tree traversal guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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