[LeetCode 388] Longest Absolute

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.extand 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.

Solution

1. 用一个map来记录每个目录/文件的层数，和其长度
2. 首先根据"\n"split给定input，得到每个目录/文件inputList。再对每个目录/文件，看其包含了几个"\t"，那么就是第几层。
3. 遍历inputList
   • 如果是目录，就在map中记录其层数和长度 （从根节点到本目录的所有长度累加）
   • 如果是文件，从map 中拿到其所在目录的directory path length， 再加上文件名长度。更新maxLength

class Solution {
    public int lengthLongestPath(String input) {
        if (input == null || input.length () == 0) {
            return 0;
        }
        
        String[] inputList = input.split ("\n");
        Map<Integer, Integer> depthVsDirLength = new HashMap<> ();
        int maxLength = 0;
        
        for (String dir : inputList) {
            int currentDepth = dir.lastIndexOf ("\t") + 1;
            int currentLength = dir.substring (currentDepth).length ();
            
            if (dir.contains (".")) {
                int filePathLength = depthVsDirLength.getOrDefault (currentDepth - 1, 0) + currentLength;
                maxLength = Math.max (maxLength, filePathLength);
            } else {
                int prevDirLength = depthVsDirLength.getOrDefault (currentDepth - 1, 0);
                depthVsDirLength.put (currentDepth, prevDirLength + currentLength + 1);
            }            
        }
        
        return maxLength;
    }
}