LeetCode 71. Simplify Path

71. Simplify Path

Difficulty: 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:

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:

1 2	Input: "/a/./b/../../c/" Output: "/c"

Example 5:

1 2	Input: "/a/../../b/../c//.//" Output: "/c"

Example 6:

1 2	Input: "/a//b////c/d//././/.." Output: "/a/b/c"

Solution

Language: Java

class Solution {
    public String simplifyPath(String path) {
        if (path == null || path.length() == 0) {
            return "";
        }
        List<String> dirs = new ArrayList<>();
        int cur = 0;
        dirs.add("");
        int start = 0;
        while (cur < path.length()) {
            char c = path.charAt(cur);
            if (c == '/') {
                while (cur + 1 < path.length() && path.charAt(cur + 1) == '/') {
                    cur++;
                }
                cur++;
            } else if (c == '.' && ((cur + 1 >= path.length() || path.charAt(cur + 1) == '/') || (cur + 1 < path.length() && path.charAt(cur + 1) == '.' && (cur + 2 >= path.length() || path.charAt(cur + 2) == '/')))) {
                if (cur + 1 < path.length() && path.charAt(cur + 1) == '.') {
                    cur++;
                    if (dirs.size() > 1) {
                        dirs.remove(dirs.size() - 1);
                    }
                }
                cur++;
            } else {
                start = cur;
                cur++;
                while (cur < path.length() && path.charAt(cur) != '/') {
                    cur++;
                }
                dirs.add(path.substring(start, cur));
            }
        }
        if (dirs.size() == 1) {
            return "/";
        }
        return String.join("/", dirs);
    }
}