388. Longest Absolute File Path
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- Total Submissions: 35565
- Difficulty: Medium
- Contributors: Admin
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. subdir2contains 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, 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) 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.
Code
class Solution(object):
def lengthLongestPath(self, input):
"""
:type input: str
:rtype: int
"""
if not input:
return 0
longest = 0
prev_tab_cnt = 0
# store tuples (name, level)
stk = []
s = input.split('\n')
for ss in s:
ss_tab_cnt = 0
while ss.startswith('\t'):
ss_tab_cnt += 1
# \t only takes one character
ss = ss[1:]
while stk and stk[-1][1] >= ss_tab_cnt:
stk.pop()
stk.append((ss, ss_tab_cnt))
if self.isfile(ss):
longest = max(longest, len('/'.join(map(lambda x: x[0], stk))))
return longest
def isfile(self, s):
if s.startswith('.') or len(s.split('.')) >= 2:
return True
else:
return False
Idea
Maintain a stack which stores the names of file/directory as well as their levels. Whenever you see it is a file name, concatenate all names in the stack. Whenever you see the current level is less than the stack top’s level, that means the previous trace has ended and the current file/directory starts from some upper level. So you need to pop stack (line 24~25).
You can change stack to dictionary. Reference: https://discuss.leetcode.com/topic/55097/simple-python-solution