LeetCode in Kotlin

1233. Remove Sub-Folders from the Filesystem

Medium

Given a list of folders folder, return the folders after removing all sub-folders in those folders. You may return the answer in any order.

If a folder[i] is located within another folder[j], it is called a sub-folder of it.

The format of a path is one or more concatenated strings of the form: '/' followed by one or more lowercase English letters.

• For example, "/leetcode" and "/leetcode/problems" are valid paths while an empty string and "/" are not.

Example 1:

Input: folder = [“/a”,”/a/b”,”/c/d”,”/c/d/e”,”/c/f”]

Output: [“/a”,”/c/d”,”/c/f”]

Explanation: Folders “/a/b” is a subfolder of “/a” and “/c/d/e” is inside of folder “/c/d” in our filesystem.

Example 2:

Input: folder = [“/a”,”/a/b/c”,”/a/b/d”]

Output: [“/a”]

Explanation: Folders “/a/b/c” and “/a/b/d” will be removed because they are subfolders of “/a”.

Example 3:

Input: folder = [“/a/b/c”,”/a/b/ca”,”/a/b/d”]

Output: [“/a/b/c”,”/a/b/ca”,”/a/b/d”]

Constraints:

• 1 <= folder.length <= 4 * 104
• 2 <= folder[i].length <= 100
• folder[i] contains only lowercase letters and '/'.
• folder[i] always starts with the character '/'.
• Each folder name is unique.

Solution

class Solution {
    fun removeSubfolders(folder: Array<String>): List<String> {
        val paths: MutableSet<String> = HashSet()
        paths.addAll(folder)
        val res: MutableList<String> = ArrayList()
        for (f in folder) {
            var lastSlash = f.lastIndexOf("/")
            var isSub = false
            while (lastSlash > 0) {
                val upperDir = f.substring(0, lastSlash)
                if (paths.contains(upperDir)) {
                    isSub = true
                    break
                }
                lastSlash = upperDir.lastIndexOf("/")
            }
            if (!isSub) {
                res.add(f)
            }
        }
        return res
    }
}

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