[LeetCode] 71. Simplify Path

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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:

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

Example 2:

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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:

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

Example 4:

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

Example 5:

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

Example 6:

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Input: "/a//b////c/d//././/.."
Output: "/a/b/c"

Explanation

  1. First, we can split the input string by "/". Then we can create a stack, iterate the array, if we see .. then we pop, otherwise we push the name of the directory to the stack.

  2. Special case is when we see the . or empty string, we ignore it. And at the end, the most inside directory name is at the top of the stack.

Solution

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class Solution {
    public String simplifyPath(String path) {
        String[] arr = path.split("/");
        Stack<String> st = new Stack<>();
        for (String str : arr) {
            if (str.equals("..")) {
                if (!st.isEmpty()) st.pop();
            }
            else if (!str.equals(".") && !str.isEmpty()) {
                st.push(str);
            }
        }
        String res = "";
        if (st.isEmpty()) return "/";
        while (!st.isEmpty()) {
            res = "/"+st.pop()+res;
        }
        return res;
    }
}