Leetcode :: Symmetric Tree

Problem

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Guess

• recursive, iterative 모두 적용해보자.
• 두 subtree 각각 left과 right, right과 left을 비교해주면 되겠다.

Sol 1. Recursive

# 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 helper(self, p, q):
        if not p and not q: return True
        if not p or not q: return False
        if p.val != q.val: return False
        
        return self.helper(p.left, q.right) and self.helper(p.right, q.left)
        
        
    def isSymmetric(self, root: TreeNode) -> bool:
        return self.helper(root.left, root.right)

Sol 2. Iterative

from collections import deque

class Solution:
    def check(self, p, q):
        if not p and not q: return True
        if not p or not q: return False
        if p.val != q.val: return False
        return True
    
    def isSymmetric(self, root: TreeNode) -> bool:
        dq = deque([(root.left, root.right)])
        
        while dq:
            p,q = dq.popleft()
            
            if not self.check(p,q):
                return False
            
            if p:
                dq.append((p.left, q.right))
                dq.append((p.right, q.left))
                
        return True