对称的二叉树

通过递归，判断左子树的左孩子跟右子树的右孩子，左子树的右孩子跟右子树的左孩子是否相等~

public class Solution {
    boolean isSymmetrical(TreeNode pRoot)
    {
        return pRoot == null || isCommon(pRoot.left,pRoot.right);
    }


    boolean isCommon(TreeNode leftNode, TreeNode rightNode){
        if(leftNode == null && rightNode == null)
            return true;
        if(leftNode == null || rightNode == null)
            return false;
        return leftNode.val==rightNode.val && isCommon(leftNode.left,rightNode.right) && isCommon(leftNode.right,rightNode.left);
    }
}