Difficulty: easy????CompletionTime: 49s

The Leetcode file system keeps a log each time some user performs a?change folder?operation.

The operations are described below:

• "../"?: Move to the parent folder of the current folder. (If you are already in the main folder,?remain in the same folder).

• "./"?: Remain in the same folder.

• "x/"?: Move to the child folder named?x?(This folder is?guaranteed to always exist).

You are given a list of strings?logs?where?logs[i]?is the operation performed by the user at the?ith?step.

The file system starts in the main folder, then the operations in?logs?are performed.

Return?the minimum number of operations needed to go back to the main folder after the change folder operations.

純模擬題，最后所在文件樹的深度即為所求結(jié)果。