Leetcode071-simplifyPath

Description

Given an absolute path for a file (Unix-style), simplify it. Or in other words, convert it to the canonical 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 the shortest string representing the absolute path.

Example

Example 1:

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Input: "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.

Example 2:

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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:

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

Example 4:

1 2	Input: "/a/./b/../../c/" Output: "/c"

Example 5:

1 2	Input: "/a/../../b/../c//.//" Output: "/c"

Example 6:

1 2	Input: "/a//b////c/d//././/.." Output: "/a/b/c"

Solution

class Solution {
    public String simplifyPath(String path) {
        Stack<String> st = new Stack<>();
        HashSet<String> set = new HashSet<>(Arrays.asList("..", ".", ""));
        for (String part: path.split("/")){
            if (part.equals("..") && !st.isEmpty()) st.pop();
            else if (!set.contains(part)) st.push(part);
        }
        String res = "";
        while(!st.isEmpty()) res = "/" + st.pop() + res;
        if (res.length() == 0) return "/";
        else return res;     
    }
}