Wednesday, April 26, 2017

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 subdir2subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1subdir2contains 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.
Thoughts:
This question gives us a string, which contains \ n and \ t this carriage return and space special characters, let us find a longest absolute file path, it should be noted that the longest absolute file path It is not necessary to have the deepest path, we can use the hash table to establish the depth and the depth of the absolute path between the length of the mapping between the current depth of the file under the absolute path is the length of the file name plus the current depth of the hash table The corresponding length, our idea is to traverse the entire string, encounter \ n or \ t to stop, and then we judge, if you encounter the carriage return, we extract this file name, if it contains'. ', That is the file, we update the res length, if it does not contain the point, that is the folder, we increase the depth level 1, and then establish the current depth and the total length of the mapping between, and then we will reset the depth level to 0. If you encounter a space before the \ t, then we add a depth, by accumulating the number of \ t, we can know the depth of the current file or folder, and then do the corresponding processing
Java Solution:
public class Solution {
    public int lengthLongestPath(String input) {
        int result = 0;
        Map map = new HashMap<>();
        map.put(0, 0);
        for(String s : input.split("\n")){
            int level = s.lastIndexOf("\t") + 1;
            int len = s.substring(level).length();
            if(s.contains(".")){
                result = Math.max(result, map.get(level) + len);
            }else{
                map.put(level + 1, map.get(level) + len + 1);
            }
        }
        return result;
    }
}

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