Leetcode #388: Longest Absolute File Path
In this guide, we solve Leetcode #388 Longest Absolute File Path in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Suppose we have a file system that stores both files and directories. An example of one system is represented in the following picture: Here, we have dir as the only directory in the root.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: Stack, Depth-First Search, String
Intuition
The problem has a natural nested or last-in-first-out structure.
A stack lets us resolve matches in the correct order as we scan.
Approach
Push items as they appear and pop when you can finalize a decision.
The stack captures the unresolved part of the input.
Steps:
- Push elements as you scan.
- Pop when a rule or match is satisfied.
- Use the stack to compute results.
Example
dir
⟶ subdir1
⟶ ⟶ file1.ext
⟶ ⟶ subsubdir1
⟶ subdir2
⟶ ⟶ subsubdir2
⟶ ⟶ ⟶ file2.ext
Python Solution
class Solution:
def lengthLongestPath(self, input: str) -> int:
i, n = 0, len(input)
ans = 0
stk = []
while i < n:
ident = 0
while input[i] == '\t':
ident += 1
i += 1
cur, isFile = 0, False
while i < n and input[i] != '\n':
cur += 1
if input[i] == '.':
isFile = True
i += 1
i += 1
# popd
while len(stk) > 0 and len(stk) > ident:
stk.pop()
if len(stk) > 0:
cur += stk[-1] + 1
# pushd
if not isFile:
stk.append(cur)
continue
ans = max(ans, cur)
return ans
Complexity
The time complexity is O(n). The space complexity is O(n).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.