leetcode-grind/problems/617/main.py

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def mergeTrees(self, t1, t2):
        # One way to do this is construct an array representing each tree and then combine them one by one
        # index is established with: 2**level + position
        # so in tree:
        #        1
        #     2     3
        #   4   5  6   7
        # The numbers shown are the indexes
        # for construction is it important to note leftChild = 2 * current
        # and rightChild = 2 * current + 1
        # The tricky part will be ensuring the array is large enough, but we can pad with None's I suppose, probably not optimal
        # but it'll do, and I think be pretty error proof
        
        # Actually scratch all this, I think it shouldn't be too hard to build the tree as we traverse both simultaneously
        # might need to make a recursive function first though
        
        return self.mergeTreesRecursive(t1, t2)
    
    def mergeTreesRecursive(self, t1, t2):
        
        # base case is neither tree has a child to add
        if t1 is None and t2 is None:
            return None
        
        if t1 is None:
            newNode = TreeNode(t2.val)
            newNode.left = self.mergeTreesRecursive(t2.left, None)
            newNode.right = self.mergeTreesRecursive(t2.right, None)
        elif t2 is None:
            newNode = TreeNode(t1.val)
            newNode.left = self.mergeTreesRecursive(t1.left, None)
            newNode.right = self.mergeTreesRecursive(t1.right, None)
        else:
            newNode = TreeNode(t1.val + t2.val)
            newNode.left = self.mergeTreesRecursive(t1.left, t2.left)
            newNode.right = self.mergeTreesRecursive(t1.right, t2.right)
            
        return newNode

s = Solution()
print("Expected: Tree with root 3") # can't be bothered testing the whole tree
t1 = TreeNode(1)
t2 = TreeNode(2)
print("Got: Tree with root", s.mergeTrees(t1, t2).val)