MockInterview: 101. Symmetric Tree

Easy

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

Solution:

Take two trees as an argument, return true if two trees are mirror.

class Solution {
    public boolean isSymmetric(TreeNode root) {
        if(root == null) return true;
        return isSymmetric(root.left,root.right);
    }
    public boolean isSymmetric(TreeNode root1, TreeNode root2){
        if(root1 == null && root2 == null){
            return true;
        }
        if(root1 == null || root2 == null){
            return false;
        }
        if(root1.val != root2.val){
            return false;
        }else{
            return isSymmetric(root1.left, root2.right) && isSymmetric(root1.right, root2.left);
        }
    }
}