1598. Crawler Log Folder

[mah-shamim]

The Leetcode file system keeps a log each time some user performs a change folder operation.

The operations are described below:

• "../" : Move to the parent folder of the current folder. (If you are already in the main folder, remain in the same folder).
• "./" : Remain in the same folder.
• "x/" : Move to the child folder named x (This folder is guaranteed to always exist).

You are given a list of strings logs where logs[i] is the operation performed by the user at the ith step.

The file system starts in the main folder, then the operations in logs are performed.

Return the minimum number of operations needed to go back to the main folder after the change folder operations.

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.

[mah-shamim]

1. Initialize a counter to keep track of the current depth of the folder hierarchy.
2. Iterate through each operation in the logs array.
3. For each operation:
   • If the operation is "../", decrement the depth counter if it's greater than zero.
   • If the operation is "./", do nothing.
   • If the operation is a folder change (i.e., it ends with "/" but isn't "./" or "../"), increment the depth counter.
4. Return the value of the depth counter, which represents the minimum number of "../" operations required to return to the main folder.

Here's the PHP implementation of this logic:

<?php
function minOperations($logs) {
    $depth = 0;

    foreach ($logs as $log) {
        if ($log == "../") {
            if ($depth > 0) {
                $depth--;
            }
        } elseif ($log != "./") {
            $depth++;
        }
    }

    return $depth;
}

// Test cases
$logs1 = ["d1/", "d2/", "../", "d21/", "./"];
$logs2 = ["d1/", "d2/", "./", "d3/", "../", "d31/"];
$logs3 = ["d1/", "../", "../", "../"];

echo minOperations($logs1); // Output: 2
echo "\n";
echo minOperations($logs2); // Output: 3
echo "\n";
echo minOperations($logs3); // Output: 0
?>

Explanation:

• The function minOperations initializes the depth variable to 0.
• It then iterates over each operation in the logs array.
• For each operation:
  • If it's "../", it decrements the depth if it's greater than zero.
  • If it's "./", it does nothing.
  • For any other folder change operation (i.e., moving to a child folder), it increments the depth.
• Finally, the function returns the current depth, which is the number of "../" operations needed to return to the main folder.