Longest Absolute File Path

LeetCode Q 388 - Longest Absolute File Path

Suppose we abstract our file system by a string in the following manner:
The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents:

dir
    subdir1
    subdir2
        file.ext

The directory dir contains an empty sub-directory subdir1 and a sub-directory subdir2 containing a file file.ext.

The string "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext" represents:

dir
    subdir1
        file1.ext
        subsubdir1
    subdir2
        subsubdir2
            file2.ext

The directory dir contains two sub-directories subdir1 and subdir2. subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1. subdir2 contains a second-level sub-directory subsubdir2 containing a file file2.ext.

We are interested in finding the longest (number of characters) absolute path to a file within our file system.

For example, in the second example above, the longest absolute path is "dir/subdir2/subsubdir2/file2.ext", and its length is 32 (not including the double quotes).If there is no file in the system, return 0.

Note:

• The name of a file contains at least a . and an extension.
• The name of a directory or sub-directory will not contain a ..
• Time complexity required: O(n) where n is the size of the input string.

Notice that a/aa/aaa/file1.txt is not the longest file path, if there is another path aaaaaaaaaaaaaaaaaaaaa/sth.png.

Solution:

1. Split the given input with \n, get a String array dirs.
2. For each dir in dirs, define its level as number of \t it contains + 1. For example, root has level 1, \ta has level 2, \t\tb has level 3.
3. Use an int array stack to store the total length at each level.
4. The key point is we keep updating the length at each level.

public int lengthLongestPath(String input) {
    if (input == null || input.length() == 0) return 0;

    String[] dirs = input.split("\n");

    int[] stack = new int[dirs.length() + 1]; 

    for (String dir: dirs) {
        int numOfTabs = dir.lastIndexOf("\t"); // \t has length 1!

        int curLen = stack[numberOfTabs] + dir.length() - numberOfTabs + 1;

        stack[numberOfTabs + 1] = curLen;

        if (dir.contains(".")) res = Math.max(res, curLen - 1);
    }

    return res;
}

Tips:

1. The length of \n, \t is 1 in Java.