Question

Formatted question description: https://leetcode.ca/all/388.html

 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).

 Given a string representing the file system in the above format, return the length of the longest absolute path to file in the abstracted file system. 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.

Algorithm

For each line, we find the position of the last space character \t, and then we can get the name of the file or folder, and then we judge whether it is a file or a folder, if it is a file, update res, if it is a folder, update HashMap mapping.

Code

Java

import java.util.HashMap;
import java.util.Map;

public class Longest_Absolute_File_Path {

    public static void main (String[] a) {
        Longest_Absolute_File_Path out = new Longest_Absolute_File_Path();
        Solution s = out.new Solution();

        //@note:
        System.out.println("abcdef".lastIndexOf("cd")); // output: 2

        String input = "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext";

        System.out.println(s.lengthLongestPath(input)); // output: 32
    }


    public class Solution {
        public int lengthLongestPath(String input) {
            int res = 0;

            // HashMap 深度 level => 当前深度的绝对路径长度 all prev path length
            Map<Integer, Integer> m = new HashMap<>();

            m.put(0, 0);

            String[] lines = input.split("\n");
            for (String s : lines) {
                // @note: s="\tsubdir1"
                //          s.charAt(0) = "\t"
                //          s.indexOf("\t") = 0
                //          s.lastIndexOf("\t") = 0
                int level = s.lastIndexOf("\t") + 1;
                int len = s.substring(level).length();
                if (s.contains(".")) {
                    res = Math.max(res, m.get(level) + len); // no +1, no `/`
                } else {
                    m.put(level + 1, m.get(level) + len + 1); // evertime a new sublevel, prev will be overwritten
                }
            }

            return res;
        }
    }
}

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