Maximum number of removals of given subsequence from a string

Given a string str, the task is to count the maximum number of possible operations that can be performed on str. An operation consists of taking a sub-sequence ‘gks’ from the string and removing it from the string.

Examples:

Input: str = "ggkssk"
Output: 1
After 1st operation: str = "gsk"
No further operation can be performed.

Input: str = "kgs"
Output: 0

Approach:



  1. Take three variables g, gk and gks which will store the occurrence of the sub-sequences ‘g’, ‘gk’ and ‘gks’ respectively.
  2. Traverse the string character by character:
    • If str[i] = ‘g’ then update g = g + 1.
    • If str[i] = ‘k’ and g > 0 then update g = g – 1 and gk = gk + 1 as previously found ‘g’ now contributes in the sub-sequence ‘gk’ along with the current ‘k’.
    • Similarly, if str[i] = ‘s’ and gk > 0 then update gk = gk – 1 and gks = gks + 1.
  3. Print the value of gks in the end.

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return max possible operation
// of the given type that can be performed on str
int maxOperations(string str)
{
    int i, g, gk, gks;
    i = g = gk = gks = 0;
    for (i = 0; i < str.length(); i++) {
        if (str[i] == 'g') {
  
            // Increment count of sub-sequence 'g'
            g++;
        }
        else if (str[i] == 'k') {
  
            // Increment count of sub-sequence 'gk'
            // if 'g' is available
            if (g > 0) {
                g--;
                gk++;
            }
        }
        else if (str[i] == 's') {
  
            // Increment count of sub-sequence 'gks'
            // if sub-sequence 'gk' appeared previously
            if (gk > 0) {
                gk--;
                gks++;
            }
        }
    }
  
    // Return the count of sub-sequence 'gks'
    return gks;
}
  
// Driver code
int main()
{
    string a = "ggkssk";
    cout << maxOperations(a);
    return 0;
}

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Java

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// Java implementation of the approach
  
class GFG
{
// Function to return max possible 
// operation of the given type that 
// can be performed on str 
static int maxOperations(String str) 
    int i, g, gk, gks; 
    i = g = gk = gks = 0
    for (i = 0; i < str.length(); i++) 
    
        if (str.charAt(i) == 'g')
        
  
            // Increment count of sub-sequence 'g' 
            g++; 
        
        else if (str.charAt(i) == 'k'
        
  
            // Increment count of sub-sequence 'gk' 
            // if 'g' is available 
            if (g > 0) { 
                g--; 
                gk++; 
            
        
        else if (str.charAt(i) == 's')
        
  
            // Increment count of sub-sequence 'gks' 
            // if sub-sequence 'gk' appeared previously 
            if (gk > 0
            
                gk--; 
                gks++; 
            
        
    
  
    // Return the count of sub-sequence 'gks' 
    return gks; 
  
// Driver code 
public static void main(String args[]) 
    String a = "ggkssk"
    System.out.print(maxOperations(a));
}
  
// This code is contributed 
// by Akanksha Rai

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Python 3

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# Python 3 implementation of the approach
  
# Function to return max possible operation
# of the given type that can be performed 
# on str
def maxOperations( str):
  
    i, g, gk, gks = 0, 0, 0, 0
    for i in range(len(str)) :
        if (str[i] == 'g') :
  
            # Increment count of sub-sequence 'g'
            g += 1
          
        elif (str[i] == 'k') :
  
            # Increment count of sub-sequence 
            # 'gk', if 'g' is available
            if (g > 0) :
                g -= 1
                gk += 1
              
        elif (str[i] == 's') :
  
            # Increment count of sub-sequence 'gks'
            # if sub-sequence 'gk' appeared previously
            if (gk > 0) :
                gk -= 1
                gks += 1
  
    # Return the count of sub-sequence 'gks'
    return gks
  
# Driver code
if __name__ == "__main__":
      
    a = "ggkssk"
    print(maxOperations(a))
  
# This code is contributed by ita_c

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C#

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// C# implementation of the approach 
using System ;
  
public class GFG{
    // Function to return max possible operation 
    // of the given type that can be performed on str 
    static int maxOperations(string str) 
    
        int i, g, gk, gks; 
        i = g = gk = gks = 0; 
        for (i = 0; i < str.Length; i++) { 
            if (str[i] == 'g') { 
      
                // Increment count of sub-sequence 'g' 
                g++; 
            
            else if (str[i] == 'k') { 
      
                // Increment count of sub-sequence 'gk' 
                // if 'g' is available 
                if (g > 0) { 
                    g--; 
                    gk++; 
                
            
            else if (str[i] == 's') { 
      
                // Increment count of sub-sequence 'gks' 
                // if sub-sequence 'gk' appeared previously 
                if (gk > 0) { 
                    gk--; 
                    gks++; 
                
            
        
      
        // Return the count of sub-sequence 'gks' 
        return gks; 
    
      
    // Driver code 
    public static void Main() 
    
        string a = "ggkssk"
        Console.WriteLine(maxOperations(a)) ;
      
    
      
}

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PHP

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<?php
// PHP implementation of the approach
  
// Function to return max possible operation
// of the given type that can be performed on str
function maxOperations($str)
{
    $i = $g = $gk = $gks = 0;
    for ($i = 0; $i < strlen($str); $i++)
    {
        if ($str[$i] == 'g')
        {
  
            // Increment count of sub-sequence 'g'
            $g++;
        }
        else if ($str[$i] == 'k')
        {
  
            // Increment count of sub-sequence 'gk'
            // if 'g' is available
            if ($g > 0) 
            {
                $g--;
                $gk++;
            }
        }
        else if ($str[$i] == 's')
        {
  
            // Increment count of sub-sequence 'gks'
            // if sub-sequence 'gk' appeared previously
            if ($gk > 0)
            {
                $gk--;
                $gks++;
            }
        }
    }
  
    // Return the count of sub-sequence 'gks'
    return $gks;
}
  
// Driver code
$a = "ggkssk";
echo maxOperations($a);
  
// This code is contributed
// by Akanksha Rai
?>

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Output:

1


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