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# Minimum number of operations required to return to the main folder

• Last Updated : 17 Jul, 2021

Given an array of strings arr[] representing the changed folder operations(Unix-style) performed on the file system. Initially, the file system opens in the main folder. The task is to find the minimum count of operations of the following three types to return to the main folder:

• “../”: Moves to the parent folder of the current folder. (If the current folder is the main folder, it remains in the same folder).
• “./”: Remains in the same folder.
• “F/”: Moves to the child folder named F.

Examples:

Input: arr[] = {“F1/”, “F2/”, “./”, “F3/”, “../”, “F31/”}
Output: 3
Explanation:
arr = “F1/”. Move to the child folder named F1. Therefore, the path of the current directory is /F1.
arr = “F2/”. Moves to the child’s folder, named F2. Therefore, the path of the current directory is /F1/F2
arr = “./” . Remains in the current folder. Therefore, the path of the current directory is /F1/F2
arr = “F3/”. Moves to the child’s folder, named F3. Therefore, the path of the current directory is /F1/F2/F3
arr = “../”. Move to the parent folder of F3. Therefore, the path of the current directory is /F1/F2
arr “F31/” . Move to the child’s folder, named F31. Therefore, the path of the current directory is /F1/F2/F31
Now, the “../” operation needs to be performed thrice to return to the main folder.
Therefore, the required output is 3.

Input: arr[] = {“F1/”, “../”, “../”}
Output: 0
Explanation:
arr = “F1/”. Therefore, the path of the current directory is /F1.
arr = “../”. Therefore, the path of the current directory is /
arr = “../”. Therefore, the path of the current directory is /
Since the current path of the directory is already in the main folder, no operations are required. Therefore, the required output is 0.

Approach: The problem can be solved using Stack. Follow the steps below to solve the problem:

• Initialize a variable, say cntOp to store the count of minimum operations required to go back to the main folder.
• Create a Stack, say st to store the path of the current folder
• Traverse the array and check the following conditions:
• If arr[i] == “../” then pop the top element of the stack.
• If arr[i] == “F/” then push the value of arr[i] on the top of the stack.
• Finally, print the count of elements left onto the stack.

Below is the implementation of the above approach:

## C++

 `// C++ program to implement``// the above approach``#include ``using` `namespace` `std;` `// Function to find minimum number of``// operations to go back to main folder``int` `minOperations(vector& arr,``                               ``int` `N)``{``    ``// Stores path of``    ``// the current folder``    ``stack st;` `    ``for` `(``int` `i = 0; i < N; i++) {``      ` `        ``// If stack is not empty and``        ``// the value of arr[i] is "../"``        ``if` `(arr[i] == ``"../"` `&&``                      ``!st.empty()) {``            ` `            ``// Pop top element of``            ``// the stack             ``            ``st.pop();``        ``}` `        ``// If the value of arr[i]``        ``// is like "F/"``        ``else` `if` `(arr[i] != ``"./"``) {``            ` `            ``// Push arr[i] on top element``            ``// of the stack              ``            ``st.push(arr[i]);``        ``}``    ``}` `    ``// Return count of elements left``    ``// into the stack``    ``return` `st.size();``}` `// Driver Code``int` `main()``{``    ``vector arr``        ``= { ``"F1/"``, ``"F2/"``, ``"./"``,``          ``"F3/"``, ``"../"``, ``"F31/"` `};``    ``int` `N = arr.size();``    ``cout << minOperations(arr, N);``}`

## Java

 `// Java program to implement``// the above approach``import` `java.util.*;` `class` `GFG{` `// Function to find minimum number of``// operations to go back to main folder``static` `int` `minOperations(String []arr, ``int` `N)``{``    ` `    ``// Stores path of``    ``// the current folder``    ``Stack st = ``new` `Stack<>();` `    ``for``(``int` `i = ``0``; i < N; i++)``    ``{``        ` `        ``// If stack is not empty and``        ``// the value of arr[i] is "../"``        ``if` `(arr[i] == ``"../"` `&& !st.empty())``        ``{``            ` `            ``// Pop top element of``            ``// the stack             ``            ``st.pop();``        ``}` `        ``// If the value of arr[i]``        ``// is like "F/"``        ``else` `if` `(arr[i] != ``"./"``)``        ``{``            ` `            ``// Push arr[i] on top element``            ``// of the stack              ``            ``st.push(arr[i]);``        ``}``    ``}` `    ``// Return count of elements left``    ``// into the stack``    ``return` `st.size();``}` `// Driver Code``public` `static` `void` `main(String args[])``{``    ``String []arr = { ``"F1/"``, ``"F2/"``, ``"./"``,``                     ``"F3/"``, ``"../"``, ``"F31/"` `};``                     ` `    ``int` `N = arr.length;``    ` `    ``System.out.print(minOperations(arr, N));``}``}` `// This code is contributed by ipg2016107`

## Python3

 `# Python3 program to implement``# the above approach` `# Function to find minimum number of``# operations to go back to main folder``def` `minOperations(arr, N):``    ` `    ``# Stores path of``    ``# the current folder``    ``st ``=` `[]` `    ``for` `i ``in` `range``(N):``        ` `        ``# If stack is not empty and``        ``# the value of arr[i] is "../"``        ``if` `(arr[i] ``=``=` `"../"` `and` `len``(st) !``=` `0``):``            ` `            ``# Pop top element of``            ``# the stack``            ``st.pop(``-``1``)` `        ``# If the value of arr[i]``        ``# is like "F/"``        ``elif` `(arr[i] !``=` `"./"``):``            ` `            ``# Push arr[i] on top element``            ``# of the stack``            ``st.append(arr[i])` `    ``# Return count of elements left``    ``# into the stack``    ``return` `len``(st)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``# Given array``    ``arr ``=` `[ ``"F1/"``, ``"F2/"``, ``"./"``,``            ``"F3/"``, ``"../"``, ``"F31/"` `]` `    ``# Size of the array``    ``N ``=` `len``(arr)` `    ``# Function Call``    ``print``(minOperations(arr, N))` `# This code is contributed by Shivam Singh`

## C#

 `// C# program to implement``// the above approach``using` `System;``using` `System.Collections.Generic;``class` `GFG{` `// Function to find minimum``// number of operations to``// go back to main folder``static` `int` `minOperations(String []arr,``                         ``int` `N)``{   ``  ``// Stores path of``  ``// the current folder``  ``Stack st =``        ``new` `Stack();` `  ``for``(``int` `i = 0; i < N; i++)``  ``{``    ``// If stack is not empty``    ``// and the value of arr[i]``    ``// is "../"``    ``if` `(arr[i] == ``"../"` `&&``        ``st.Count != 0)``    ``{``      ``// Pop top element of``      ``// the stack             ``      ``st.Pop();``    ``}` `    ``// If the value of arr[i]``    ``// is like "F/"``    ``else` `if` `(arr[i] != ``"./"``)``    ``{` `      ``// Push arr[i] on top``      ``// element of the stack              ``      ``st.Push(arr[i]);``    ``}``  ``}` `  ``// Return count of elements``  ``// left into the stack``  ``return` `st.Count;``}` `// Driver Code``public` `static` `void` `Main(String []args)``{``  ``String []arr = {``"F1/"``, ``"F2/"``, ``"./"``,``                  ``"F3/"``, ``"../"``, ``"F31/"``};``  ``int` `N = arr.Length;``  ``Console.Write(minOperations(arr, N));``}``}` `// This code is contributed by gauravrajput1`

## Javascript

 ``

Output:

`3`

Time Complexity: O(N)
Auxiliary Space: O(N)

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