Invert Binary Tree

• Difficulty: Easy
• Primary pattern: Trees
• Tags: Tree, Depth-First Search, Breadth-First Search, Binary Tree
• Time taken: 04:11
• LeetCode Link

Key Idea

• Recursion
• Break down problem to sub problem, that has a pattern that can be solved in a sub function

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 invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        # Recursion
            # This is a tree graph, we need to make right = left, and left = right
        if not root:
            return None
        # Recursive Call
        root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)
        return root

Complexity

• Time: O(n) - Every node is visited exactly once
• Space: O(h) - height of the tree dependency