LeetCode Link: 101 Symmetric Tree
Language: C#
Problem Statement
Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).
Examples
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
Constraints
- The number of nodes in the tree is in the range [1, 1000].
- -100 <= Node.val <= 100
Solution
/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution
{
public bool IsSymmetric(TreeNode root)
{
if (root is null)
{
return true;
}
return Sym(root.left, root.right);
}
private bool Sym(TreeNode l, TreeNode r)
{
if (l is null && r is null)
{
return true;
}
if (l is null || r is null)
{
return false;
}
if (l.val != r.val)
{
return false;
}
return Sym(l.left, r.right) && Sym(l.right, r.left);
}
}
Complexity
Time Complexity: O(N)
Space Complexity: O(1)