Simplify Path

String, Stack

Medium

Given anabsolute pathfor a file (Unix-style), simplify it. Or in other words, convert it to thecanonical path.

In a UNIX-style file system, a period. refers to the current directory. Furthermore, a double period.. moves the directory up a level. For more information, see: Absolute path vs relative path in Linux/Unix

Note that the returned canonical path must always begin with a slash/, and there must be only a single slash/ between two directory names. The last directory name (if it exists)must not end with a trailing/. Also, the canonical path must be theshorteststring representing the absolute path.

Example 1:

Input: "
/home/"
Output: "
/home"

Explanation:
 Note that there is no trailing slash after the last directory name.

Example 2:

Input: "
/../"
Output: "
/"
Explanation:
 Going one level up from the root directory is a no-op, as the root level is the highest level you can go.

Example 3:

Input: "
/home//foo/"
Output: "
/home/foo"
Explanation: 
In the canonical path, multiple consecutive slashes are replaced by a single one.

Example 4:

Input: "
/a/./b/../../c/"
Output: "
/c"

Example 5:

Input: "
/a/../../b/../c//.//"
Output: "
/c"

Example 6:

Input: "
/a//b////c/d//././/.."
Output: "
/a/b/c"

Solution & Analysis

Stack + String Split + String Concatenation

@shpolsky https://leetcode.com/problems/simplify-path/discuss/25686/Java-10-lines-solution-with-stack

The main idea is to push to the stack every valid file name (not in {"",".",".."}), popping only if there's smth to pop and we met "..". I don't feel like the code below needs any additional comments.

13 ms, faster than 73.84%

class Solution {
    public String simplifyPath(String path) {
        Deque<String> stack = new LinkedList<>();
        Set<String> skip = new HashSet<>(Arrays.asList("..",".",""));
        for (String dir : path.split("/")) {
            if (dir.equals("..") && !stack.isEmpty()) stack.pop();
            else if (!skip.contains(dir)) stack.push(dir);
        }
        String res = "";
        for (String dir : stack) res = "/" + dir + res;
        return res.isEmpty() ? "/" : res;
    }
}