lintcode-->等价二叉树

public boolean isIdentical(TreeNode a, TreeNode b) {        // Write your code here        if(a == null && b == null){            return true;        }        if(a!=null && b!=null){            if(a.val == b.val){                return isIdentical(a.left,b.left) && isIdentical(a.right, b.right);            } else {                return false;            }        }        return false;    }