longest-absolute-file-path.py

# Time:  O(n)
# Space: O(d), d is the max depth of the paths

# 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.


class Solution(object):
    def lengthLongestPath(self, input):
        """
        :type input: str
        :rtype: int
        """
        def split_iter(s, tok):
            start = 0
            for i in xrange(len(s)):
                if s[i] == tok:
                    yield s[start:i]
                    start = i + 1
            yield s[start:]


        max_len = 0
        path_len = {0: 0}
        for line in split_iter(input, '\n'):
            name = line.lstrip('\t')
            depth = len(line) - len(name)
            if '.' in name:
                max_len = max(max_len, path_len[depth] + len(name))
            else:
                path_len[depth + 1] = path_len[depth] + len(name) + 1
        return max_len