# Simplify Path

`String`, `Stack`

**Medium**

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](https://www.linuxnix.com/abslute-path-vs-relative-path-in-linuxunix/)

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"
```

## 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%

```java
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;
    }
}
```