Python Code to Build Tree and Get Paths

Build Binary Tree and Get Root-to-Leaf Paths

class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None


def build_tree(arr):
    if not arr:
        return None
    
    nodes = [TreeNode(v) for v in arr]
    
    for i in range(len(arr)):
        left = 2*i + 1
        right = 2*i + 2
        
        if left < len(arr):
            nodes[i].left = nodes[left]
        if right < len(arr):
            nodes[i].right = nodes[right]
    
    return nodes[0]


def root_to_leaf_paths(root):
    paths = []
    
    def dfs(node, path):
        if not node:
            return
        
        path.append(node.val)
        
        if not node.left and not node.right:
            paths.append(list(path))
        else:
            dfs(node.left, path)
            dfs(node.right, path)
        
        path.pop()
    
    dfs(root, [])
    return paths


# Example
arr = [1,0,1,0,2,3,4]
root = build_tree(arr)
print(root_to_leaf_paths(root))
        

LeetCode Style Solution: Sum Root to Leaf Binary Numbers

# Definition for a binary tree node.
from typing import Optional

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: Optional[TreeNode]) -> int:
        # Minimal check for empty tree
        if not root:
            return 0
        
        # Just return the root-to-leaf sum using the helper
        return self.root_to_leaf_paths(root)

    
    def root_to_leaf_paths(self, root: Optional[TreeNode]) -> int:
        paths = []

        def dfs(node, path):
            if not node:
                return

            path.append(node.val)

            if not node.left and not node.right:
                paths.append(list(path))
            else:
                dfs(node.left, path)
                dfs(node.right, path)

            path.pop()

        dfs(root, [])

        decimal = 0
        for path in paths:
            decimal += int("".join(map(str, path)), 2)

        return decimal


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

def buildTree(arr):
    if not arr:
        return None

    nodes = [TreeNode(v) for v in arr]

    for i in range(len(arr)):
        left = 2*i + 1
        right = 2*i + 2

        if left < len(arr):
            nodes[i].left = nodes[left]
        if right < len(arr):
            nodes[i].right = nodes[right]

    return nodes[0]


arr = buildTree(root)
sol = Solution()
print(sol.sumRootToLeaf(arr))