0388. Longest Absolute File Path

https://leetcode.com/problems/longest-absolute-file-path

Description

Suppose we have a file system that stores both files and directories. An example of one system is represented in the following picture:

Here, we have dir as the only directory in the root. dir contains two subdirectories, subdir1 and subdir2. subdir1 contains a file file1.ext and subdirectory subsubdir1. subdir2 contains a subdirectory subsubdir2, which contains a file file2.ext.

In text form, it looks like this (with ⟶ representing the tab character):

dir
⟶ subdir1
⟶ ⟶ file1.ext
⟶ ⟶ subsubdir1
⟶ subdir2
⟶ ⟶ subsubdir2
⟶ ⟶ ⟶ file2.ext

If we were to write this representation in code, it will look like this: "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext". Note that the '\n' and '\t' are the new-line and tab characters.

Every file and directory has a unique absolute path in the file system, which is the order of directories that must be opened to reach the file/directory itself, all concatenated by '/'s. Using the above example, the absolute path to file2.ext is "dir/subdir2/subsubdir2/file2.ext". Each directory name consists of letters, digits, and/or spaces. Each file name is of the form name.extension, where name and extension consist of letters, digits, and/or spaces.

Given a string input representing the file system in the explained format, return the length of the longest absolute path to a file in the abstracted file system. If there is no file in the system, return 0.

Example 1:

**Input:** input = "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext"
**Output:** 20
**Explanation:** We have only one file, and the absolute path is "dir/subdir2/file.ext" of length 20.

Example 2:

**Input:** input = "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext"
**Output:** 32
**Explanation:** We have two files:
"dir/subdir1/file1.ext" of length 21
"dir/subdir2/subsubdir2/file2.ext" of length 32.
We return 32 since it is the longest absolute path to a file.

Example 3:

**Input:** input = "a"
**Output:** 0
**Explanation:** We do not have any files, just a single directory named "a".

Example 4:

**Input:** input = "file1.txt\nfile2.txt\nlongfile.txt"
**Output:** 12
**Explanation:** There are 3 files at the root directory.
Since the absolute path for anything at the root directory is just the name itself, the answer is "longfile.txt" with length 12.

Constraints:

• 1 <= input.length <= 104

• input may contain lowercase or uppercase English letters, a new line character '\n', a tab character '\t', a dot '.', a space ' ', and digits.

ac

class Solution {
    public int lengthLongestPath(String input) {
        Stack<Integer> stack = new Stack<>();
        stack.push(0); // dummy node, convenient to peek

        int max = 0;
        for (String s : input.split("\n")) {
            int level = s.lastIndexOf("\t") + 1;
            int len = s.length() - level;
            while (stack.size() - 1 > level) stack.pop();
            // check if file
            if (s.contains(".")) {
                max = Math.max(max, stack.peek() + len);
            } else {
                stack.push(stack.peek() + len + 1); // dir/ -> dir/subdir2/
            }
        }

        return max;
    }
}
/*
use stack to store every level's length, when meet file (with .) update max length.
key: know current level
*/