101_SymmetricTree.md

101. Symmetric Tree

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

Example 1:

Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:

Input: root = [1,2,2,null,3,null,3]
Output: false

Clarification:

The number of nodes in the tree is in the range [1, 1000].
-100 <= Node.val <= 100

Solution:

• Recursive

code:

• java

  • Code

    class Solution {
        public boolean isSymmetric(TreeNode root) {
            if(root==null){
                return true;
            }
            return isSymmetricHelp(root.left, root.right);
        }
    
        private boolean isSymmetricHelp(TreeNode left, TreeNode right){
            if(left==null || right==null){
                return left==right;
            }
            if(left.val!=right.val){
                return false;
            }
            return isSymmetricHelp(left.left, right.right) && isSymmetricHelp(left.right, right.left);
        }
    }

• python

  class Solution: