grid47 Exploring patterns and algorithms
Sep 29, 2024
6 min read
Solution to LeetCode 388: Longest Absolute File Path Problem
In a file system where both directories and files are stored, we are given a string representation of the system. The string includes the directory structure, with tab characters (’\t’) representing subdirectories and newline characters (’\n’) representing file and directory boundaries. Each directory and file has a unique absolute path. Compute the length of the longest absolute path to a file. If no file exists, return 0.
Problem
Approach
Steps
Complexity
Input: The input is a string representing the file system's directory and file structure, with directories and files separated by newline ('\n') characters, and subdirectories indicated by tab ('\t') characters.
• Explanation: The longest file path is 'root/subfolder2/file1.txt', which has a length of 21.
Approach: We will use a stack to track the length of the current path as we process each directory or file. When we encounter a file, we calculate its total path length and check if it is the longest file path encountered so far.
Observations:
• We need to differentiate between directories and files, which can be done by checking for a dot ('.') in the name.
• We can iterate through the string, updating the current path length as we encounter new levels of directories and calculating the file's path length when we find a file.
Steps:
• Initialize a stack to track the length of the current path at each directory level.
• Iterate through the input string character by character.
• If a tab is encountered, increase the level of the current directory.
• If a newline is encountered, process the current level and reset the current directory's length.
• When a file is encountered, calculate the total length of the path and update the maximum length if necessary.
Empty Inputs:
• Empty input will not be provided as per the problem statement.
Large Inputs:
• Ensure that the algorithm handles inputs with the maximum allowed length efficiently.
Special Values:
• The input may consist only of directories, in which case the result should be 0.
Constraints:
• Ensure the algorithm handles deeply nested structures and large numbers of files.
intlengthLongestPath(string ipt) {
vector<int> levels(300, 0);
int level =0;
bool isFile =false;
int ans =0;
int len =0;
for(charc: ipt) {
switch(c) {
case'\n': level =0, isFile =false, len =0; break;
case'\t': level++; break;
case'.': isFile =true;
default: len++;
levels[level] = len;
if(isFile) {
ans = max(ans, accumulate(levels.begin(), levels.begin() + level +1, 0) + level);
}
}
}
return ans;
}
1 : Function Definition
intlengthLongestPath(string ipt) {
Define the function 'lengthLongestPath' that takes a string 'ipt' representing a directory structure and returns the length of the longest path to a file.
2 : Data Structure
vector<int> levels(300, 0);
Declare a vector 'levels' to store the length of the current path at each level (up to 300 levels).
3 : Variable Initialization
int level =0;
Initialize 'level' to keep track of the current level in the directory structure.
4 : Variable Initialization
bool isFile =false;
Initialize 'isFile' to check if the current string represents a file.
5 : Variable Initialization
int ans =0;
Initialize 'ans' to store the length of the longest file path.
6 : Variable Initialization
int len =0;
Initialize 'len' to store the current length of the path being processed.
7 : Loop Iteration
for(charc: ipt) {
Start a loop to iterate through each character in the input string 'ipt'.
8 : Switch Case
switch(c) {
Use a switch-case statement to handle different types of characters (newlines, tabs, periods, and others).
9 : Case Handling
case'\n':
Handle the case when a newline character is encountered.
10 : Reset Variables
level =0, isFile =false, len =0; break;
Reset the variables 'level', 'isFile', and 'len' when encountering a newline character.
11 : Case Handling
case'\t':
Handle the case when a tab character is encountered.
12 : Level Increase
level++; break;
Increase the 'level' when a tab character is encountered (indicating a deeper directory level).
13 : Case Handling
case'.':
Handle the case when a period character is encountered (indicating a file).
14 : File Check
isFile =true;
Set 'isFile' to true when a period character is encountered, indicating that the current string is a file.
15 : Default Case
default:
Handle the default case for non-special characters (normal directory or file name characters).
16 : Path Length Calculation
len++;
Increment the 'len' for each character that is part of a directory or file name.
17 : Path Length Calculation
levels[level] = len;
Store the current path length at the given 'level'.
