71. Simplify Path

• Difficulty: Medium

• Topics: String, Stack

• Similar Questions:

Problem:

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"

Solutions:

class Solution {
public:
    string simplifyPath(string path) {
        path.push_back('/'); // an elegant solution for last element
        deque<string> dq; // deque is more appropriate than stack because the result need queue-like access. 
        string directory;
        for (int i = 0; i < path.length(); ++i) {
            if (path[i] == '/') {
                if (directory == "" || directory == ".") {
                    ;
                } else if (directory == "..") {
                    if (!dq.empty()) {
                        dq.pop_back();
                    }
                } else {
                    dq.push_back(directory);
                }
                directory.clear();
            } else {
                directory.push_back(path[i]);
            }
        }

        if (dq.empty())    return "/";
        string ret;

        while (!dq.empty()) {
            ret.push_back('/');
            ret.append(dq.front()); dq.pop_front();
        }

        return ret;
    }
};