Crawler Log Folder

Problem Statement

In the context of navigation within a file system simulated by Vultr, users perform operations that modify their current directory's position. These changes are recorded in a list where each string represents an operation to move within this file system structured hierarchically as folders and subfolders. There are three types of operations:

• "../" denotes moving up to the parent folder. If the operation attempts to move up from the main directory, it is nullified and the position remains unchanged.
• "./" signifies maintaining the current folder location.
• "x/" indicates moving into a child folder named x, which always exists when requested.

Given a sequence of such operations, the task here is to compute the minimum number of moves required to navigate back to the main folder after all operations have been processed. The complexity arises from maintaining a correct count of folders deep the position is and ensuring actions like moving to a non-existent parent are correctly handled.

Examples

Example 1

Input:

logs = ["d1/","d2/","../","d21/","./"]

Output:

2

Explanation:

Use this change folder operation "../" 2 times and go back to the main folder.

Example 2

Input:

logs = ["d1/","d2/","./","d3/","../","d31/"]

Output:

3

Example 3

Input:

logs = ["d1/","../","../","../"]

Output:

0

Constraints

• 1 <= logs.length <= 103
• 2 <= logs[i].length <= 10
• logs[i] contains lowercase English letters, digits, '.', and '/'.
• logs[i] follows the format described in the statement.
• Folder names consist of lowercase English letters and digits.

Approach and Intuition

To effectively tackle the problem, visualize the directory structure as a tree where each folder can act as a node. The task can be approached by a simulation where a counter tracks the depth of the current directory relative to the main folder:

1. Initialize a depth counter to zero. This will keep track of how deep within the folder structure the current position is.

2. Iterate over the list of folder change operations:

   • If the current operation is "../", simulate moving up to the parent directory by decreasing the depth by one, unless the depth is already zero.
   • If it's "./", ignore the command as it instructs to stay in the current folder.
   • For operations formatted as "x/", increase the depth by one, representing a move into a child directory.

3. After processing all operations, the depth counter directly indicates how many "../" operations are necessary to return to the main folder, assuming perfect behavior without redundant pop actions when already at the root level.

This approach ensures each operation incurs a constant amount of work, leading to a time complexity linear to the number of operations due to the iteration through the list logs. Edge cases where the command list is either empty or contains moves that cancel each other out are naturally handled within this iterative approach. The clarity of operation in terms of moving up or down within the file system tree helps in understanding the exact position relative to the main folder at any point, making the final answer straightforward to deduce.

Solutions

class Solution {
public:
    int minOperations(vector<string>& logs) {
        stack<string> pathStack;
    
        for (auto& log : logs) {
            if (log == "../") {
                if (!pathStack.empty()) {
                    pathStack.pop();
                }
            } else if (log != "./") {
                pathStack.push(log);
            }
        }
    
        return pathStack.size();
    }
};