← 返回 citadel 的题目列表Lazy Deletion Valid Token
类型：online_judge
Given a sequence of operations, determine if delete operations' tokens are still valid.
Input: A list of string operations operations, such as add token, delete token, isExist token.
Output: Return true if all delete token operations occur after their corresponding isExist token; otherwise, return false.
Example
Input
3
add a
delete a
isExist a
Output
false