Given a string path, which is an absolute path (starting with a slash '/') to a file or directory in a Unix-style file system, convert it to the simplified canonical path.

In a Unix-style file system, a period '.' refers to the current directory, a double period '..' refers to the directory up a level, and any multiple consecutive slashes (i.e. '//') are treated as a single slash '/'. For this problem, any other format of periods such as '...' are treated as file/directory names.

The canonical path should have the following format:

The path starts with a single slash '/'.
Any two directories are separated by a single slash '/'.
The path does not end with a trailing '/'.
The path only contains the directories on the path from the root directory to the target file or directory (i.e., no period '.' or double period '..')
Return the simplified canonical path.

Example 1:

Input: path = "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.
Example 2:

Input: path = "/../"
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: path = "/home//foo/"
Output: "/home/foo"
Explanation: In the canonical path, multiple consecutive slashes are replaced by a single one.
Example 4:

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

Constraints:

1 <= path.length <= 3000
path consists of English letters, digits, period '.', slash '/' or '_'.
path is a valid absolute Unix path.

來源：力扣（LeetCode）
連結：https://leetcode-cn.com/problems/simplify-path

    public String simplifyPath(String path) {
        /**
        pop(): 彈出棧中元素，也就是返回並移除隊頭元素，等價於removeFirst()，
        如果佇列無元素，則發生NoSuchElementException

        push(): 向棧中壓入元素，也就是向隊頭增加元素，等價於addFirst()，
        如果元素為null，則發生NPE，如果棧空間受到限制，則發生IllegalStateException
        */ 
        Deque<String> stack = new LinkedList<>();
        for (String s : path.split("/")) {
            if (s.equals("..")) {
                if (!stack.isEmpty()) {
                    stack.pop();  // deque中彈出隊頭元素
                }
                
            } else if (!s.isEmpty() && !s.equals(".")) {
                stack.push(s);  // 在隊頭插入
            }
        }
        
        System.out.println(stack);
        
        String res = "";
        for (String s : stack) {
            System.out.println(s);
            res = "/" + s + res;
            System.out.println(res);
        }
        
        return res.isEmpty() ? "/" : res;
        
    }````