71. Simplify Path

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 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"
class Solution {
    public String simplifyPath(String path) {
        String[] strs = path.split("/");
        ArrayList<String> list1 = new ArrayList<String>();
        for(int i = 0; i < strs.length; i++){
        //将空字符串(由类似这种"/a//c"的字符串产生)和 "." ("."代表当前目录不影响路径)去掉,保存到 list1
        if (strs[i].isEmpty() || strs[i].equals(".")) {
        ArrayList<String> list2 = new ArrayList<String>();
        for(int i = 0; i < list1.size(); i++){
                    list2.remove(list2.size() - 1);
            } else list2.add(list1.get(i));
        String res = String.join("/",list2);
        res = "/" + res;
        return res;