Leetcode Problem 101 Symmetric tree.txt

101. Symmetric Tree
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:

    1
   / \
  2   2
 / \ / \
3  4 4  3
 

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

    1
   / \
  2   2
   \   \
   3    3
 

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


Hint to solve: Make a recurive function that checks for until both nodes are null, one of the nodes is null. Make recurive call for left,right and right,left with comparing the current two parent's value.


/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    bool isMirror(TreeNode leftNode, TreeNode rightNode)
    {
        if(leftNode == null && rightNode == null)
            return true;
        
        if(leftNode == null || rightNode == null)
            return false;
               
        return (leftNode.val == rightNode.val) && isMirror(leftNode.left,rightNode.right) && isMirror(leftNode.right,rightNode.left);
    }
    
    public bool IsSymmetric(TreeNode root) 
    {
        if(root == null)
            return true;
        
        return isMirror(root.left,root.right);
    }
    
}