Minimum number of replacement done of substring "01" with "110" to remove it completely

Given a binary string S, the task is to find the minimum number of repetitive replacements of substring "01" to string "110" such that there doesn't exist any substring "01" in the given string S.

Examples:

Input: S = "01"
Output: 1
Explanation:
Below are the operations performed:
Operation 1: Choosing substring (0, 1) in the string "01" and replacing it with "110" modifies the given string to "110".
After the above operations, the string S(= "110") doesn't contain any substring as "01". Therefore, the total number of operation required is 1.

Input: S = "001"
Output:3
Explanation:
Below are the operations performed:
Operation 1: Choosing substring (1, 2) in the string "001" and replacing it with "110" modifies the given string to "0110".
Operation 2: Choosing substring (0, 1) in the string "0110" and replacing it with "110" modifies the given string to "11010".
Operation 3: Choosing substring (2, 3) in the string "11010" and replacing it with "110" modifies the given string to "111100".
After the above operations, the string S(= "111100") doesn't contain any substring as "01". Therefore, the total number of operation required is 3.

Approach: The given problem can be solved using the Greedy Approach. The operation is whenever a substring "01" is found it is replaced with "110" and now the number of '1' is present on the right side of this '0' forms substring "01" which takes part in changing the string to "110". Therefore, the idea is to traverse the string from the end and whenever '0' occurs, perform the given operation until the number of 1s present on the right side. Follow the steps below to solve the problem:

• Initialize two variables, say ans and cntOne both as 0 to store the minimum number of operations performed and count of consecutive 1s from the end during traversal.
• Traverse the given string S from the end and perform the following steps:
  • If the current character is 0, then increment the ans by the number of consecutive 1s obtained till now and twice the value of the count of consecutive 1s.
  • Otherwise, increment the value of cntOne by 1.
• After completing the above steps, print the value of ans as the minimum number of operations.

Below is the implementation of the above approach:

// C++ program for the above approach

#include <bits/stdc++.h>

using namespace std;

// Function to find the minimum number
// of replacement of "01" with "110"
// s.t. S doesn't contain substring "10"
void minimumOperations(string S, int N)
{
    // Stores the number of operations
    // performed
    int ans = 0;

    // Stores the resultant count
    // of substrings
    int cntOne = 0;

    // Traverse the string S from end
    for (int i = N - 1; i >= 0; i--) {

        // If the current character
        // is 0
        if (S[i] == '0') {
            ans += cntOne;
            cntOne *= 2;
        }

        // If the current character
        // is 1
        else
            cntOne++;
    }

    // Print the result
    cout << ans;
}

// Driver Code
int main()
{
    string S = "001";
    int N = S.length();
    minimumOperations(S, N);

    return 0;
}

// Java program for the above approach

import java.io.*;

class GFG {
    // Function to find the minimum number
    // of replacement of "01" with "110"
    // s.t. S doesn't contain substring "10"
    public static void minimumOperations(String S, int N)
    {
        // Stores the number of operations
        // performed
        int ans = 0;

        // Stores the resultant count
        // of substrings
        int cntOne = 0;

        // Traverse the string S from end
        for (int i = N - 1; i >= 0; i--) {

            // If the current character
            // is 0
            if (S.charAt(i) == '0') {
                ans += cntOne;
                cntOne *= 2;
            }

            // If the current character
            // is 1
            else
                cntOne++;
        }

        // Print the result
        System.out.println(ans);
    }

    // Driver Code
    public static void main(String[] args)
    {
        String S = "001";
        int N = S.length();
        minimumOperations(S, N);
    }
}

  // This code is contributed by Potta Lokesh

# Python3 program for the above approach

# Function to find the minimum number
# of replacement of "01" with "110"
# s.t. S doesn't contain substring "10"
def minimumOperations(S, N):
    
    # Stores the number of operations
    # performed
    ans = 0

    # Stores the resultant count
    # of substrings
    cntOne = 0

    # Traverse the string S from end
    i = N - 1
    
    while(i >= 0):
        
        # If the current character
        # is 0
        if (S[i] == '0'):
            ans += cntOne
            cntOne *= 2

        # If the current character
        # is 1
        else:
            cntOne += 1
            
        i -= 1

    # Print the result
    print(ans)

# Driver Code
if __name__ == '__main__':
    
    S = "001"
    N = len(S)
    
    minimumOperations(S, N)

# This code is contributed by ipg2016107

// C# program for the above approach
using System;

class GFG{

// Function to find the minimum number
// of replacement of "01" with "110"
// s.t. S doesn't contain substring "10"
public static void minimumOperations(string S, int N)
{
    
    // Stores the number of operations
    // performed
    int ans = 0;

    // Stores the resultant count
    // of substrings
    int cntOne = 0;

    // Traverse the string S from end
    for(int i = N - 1; i >= 0; i--) 
    {
        
        // If the current character
        // is 0
        if (S[i] == '0') 
        {
            ans += cntOne;
            cntOne *= 2;
        }

        // If the current character
        // is 1
        else
            cntOne++;
    }

    // Print the result
    Console.WriteLine(ans);
}

// Driver code
static void Main()
{
    string S = "001";
    int N = S.Length;
    
    minimumOperations(S, N);
}
}

// This code is contributed by abhinavjain194

 <script>
        // JavaScript program for the above approach

        // Function to find the minimum number
        // of replacement of "01" with "110"
        // s.t. S doesn't contain substring "10"
        function minimumOperations(S, N)
        {
        
            // Stores the number of operations
            // performed
            let ans = 0;

            // Stores the resultant count
            // of substrings
            let cntOne = 0;

            // Traverse the string S from end
            for (let i = N - 1; i >= 0; i--) {

                // If the current character
                // is 0
                if (S[i] == '0') {
                    ans += cntOne;
                    cntOne *= 2;
                }

                // If the current character
                // is 1
                else
                    cntOne++;
            }

            // Print the result
            document.write(ans);
        }

        // Driver Code

        let S = "001";
        let N = S.length;
        minimumOperations(S, N);

  // This code is contributed by Potta Lokesh
    </script>

3

Time Complexity: O(N)
Auxiliary Space: O(1)