Symmetric Tree

recursion programming

public class Solution {
    public boolean isSymmetric(TreeNode root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == null)
            return true;
        return checkTwoSubtree(root.left, root.right);
    }
    private boolean checkTwoSubtree(TreeNode leftTree, TreeNode rightTree)
    {
        if(leftTree == null && rightTree == null)
            return true;
        if(leftTree == null || rightTree == null)
            return false;
        if(leftTree.val != rightTree.val)
            return false;
        return checkTwoSubtree(leftTree.left, rightTree.right) && checkTwoSubtree(leftTree.right, rightTree.left);
    }
}