花花酱 LeetCode 101. Symmetric Tree

zxi — Fri, 27 Jul 2018 04:18:30 +0000

Problem

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

But the following [1,2,2,null,3,null,3] is not:

Note:
Bonus points if you could solve it both recursively and iteratively.

Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)

C++

class Solution {
public:
  bool isSymmetric(TreeNode* root) {
    return isMirror(root, root);
  }
private:
  bool isMirror(TreeNode* root1, TreeNode* root2) {
    if (!root1 && !root2) return true;
    if (!root1 || !root2) return false;
    return root1->val == root2->val 
           && isMirror(root1->right, root2->left) 
           && isMirror(root1->left, root2->right);
  }
};

Python

"""
Author: Huahua
Running time: 48 ms
"""
class Solution:
  def isSymmetric(self, root):
    def isMirror(root1, root2):
      if not root1 and not root2: return True
      if not root1 or not root2: return False
      return root1.val == root2.val \
        and isMirror(root1.left, root2.right) \
        and isMirror(root2.left, root1.right)
    return isMirror(root, root)

symmetric Archives - Huahua's Tech Road

花花酱 LeetCode 101. Symmetric Tree

Problem

Solution: Recursion

C++

Python

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