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 directorydircontains an empty sub-directorysubdir1and a sub-directorysubdir2containing a filefile.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 directorydircontains two sub-directoriessubdir1andsubdir2.subdir1contains a filefile1.extand an empty second-level sub-directorysubsubdir1.subdir2contains a second-level sub-directorysubsubdir2containing a filefile2.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 is32(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, return0.

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)wherenis the size of the input string.

Notice thata/aa/aaa/file1.txtis not the longest file path, if there is another pathaaaaaaaaaaaaaaaaaaaaa/sth.png.

public class Solution {
    public int lengthLongestPath(String input) {
        if(input.length() == 0) return 0;
        String[] items = input.split("\n");
        List<Integer> path = new ArrayList<Integer>();
        int max = 0;
        for(int i = 0; i < items.length; i++) {
            int level = 0;
            int nameStart = 0;
            while(nameStart < items[i].length() && items[i].charAt(nameStart) == '\t') {
                level ++;
                nameStart += 1;
            }

            while(path.size() > level) {
                path.remove(path.size() - 1);
            }

            path.add(items[i].length() - nameStart);


            if(items[i].indexOf('.') != -1) {
                int sum = 0;
                for(Integer len: path) sum += len;
                sum += path.size() - 1;
                max = Integer.max(sum, max);
            }
        }
        return max;
    }
}