[LeetCode] 71. Simplify Path

Problem

Given an absolute path for a file (Unix-style), simplify it.

For example,

path = "/home/", => "/home"
path = "/a/./b/../../c/", => "/c"
path = "/a/../../b/../c//.//", => "/c"        //here: b is cancelled out, a is cancelled out
path = "/a//b////c/d//././/..", => "/a/b/c"   //here d is cancelled out

In a UNIX-style file system, a period ('.') refers to the current directory, so it can be ignored in a simplified path. Additionally, a double period ("..") moves up a directory, so it cancels out whatever the last directory was. For more information, look here: https://en.wikipedia.org/wiki...

Corner Cases:

Did you consider the case where path = "/../"?
In this case, you should return "/".
Another corner case is the path might contain multiple slashes '/' together, such as "/home//foo/".
In this case, you should ignore redundant slashes and return "/home/foo".

Solution

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