# 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"

# Solution

Approach 1: Two pointers.

# Code (Python)

Approach 1:

# Code (C++)

Approach 1:

class Solution {
public:
    string simplifyPath(string path) {
        stack<string> dirs;
        int head = 0;
        int tail = 0;
        while (tail <= path.size())
        {
            if (tail == path.size() || path[tail] == '/') // "tail == path.size()".
            {
                if (tail > head)
                {
                    string dir = path.substr(head, tail - head);
                    if (dir != ".." && dir != ".")
                        dirs.push(dir);
                    else if (dir == ".." && !dirs.empty())
                        dirs.pop();
                }
                head = tail + 1;
            }
            tail++;
        }
        if (dirs.empty())
            return "/";
        string simplifiedPath;
        while (!dirs.empty())
        {
            simplifiedPath = "/" + dirs.top() + simplifiedPath;
            dirs.pop();
        }
        return simplifiedPath;
    }
};