Minimum characters that are to be inserted such that no three consecutive characters are same

Given a string str and the task is to modify the string such that no three consecutive characters are same. In a single operation, any character can be inserted at any position in the string. Find the minimum number of such operations required.

Examples:

Input : str = “aabbbcc”
Output: 1
“aabbdbcc” is the modified string.



Input: str = “geeksforgeeks”
Output: 0

Approach: For every three consecutive characters which are same, a single character has to be inserted in between them to make any three consecutive characters different. But the number of operations needs to be minimized so the character must be inserted after the second character. For example, if the string is “bbbb” then if the character is inserted at the second position i.e. “babbb” then there are still three consecutive same characters and another operation is required to resolve that but if the character was inserted at the third position i.e. “bbabb” then only a single operation is required.

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 the count of characters
// that are to be inserted in str such that no
// three consecutive characters are same
int getCount(string str, int n)
{
  
    // To store the count of
    // operations required
    int cnt = 0;
  
    int i = 0;
    while (i < n - 2) {
  
        // A character needs to be
        // inserted after str[i + 1]
        if (str[i] == str[i + 1]
            && str[i] == str[i + 2]) {
            cnt++;
            i = i + 2;
        }
  
        // Current three consecutive
        // characters are not same
        else
            i++;
    }
  
    return cnt;
}
  
// Driver code
int main()
{
    string str = "aabbbcc";
    int n = str.length();
  
    cout << getCount(str, n);
  
    return 0;
}

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Java

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// Java implementation of the approach
import java.util.*;
  
class GFG
{
      
    // Function to return the count of characters
    // that are to be inserted in str such that no
    // three consecutive characters are same
    static int getCount(char[] str, int n)
    {
  
        // To store the count of
        // operations required
        int cnt = 0;
  
        int i = 0;
        while (i < n - 2
        {
  
            // A character needs to be
            // inserted after str[i + 1]
            if (str[i] == str[i + 1] && 
                str[i] == str[i + 2]) 
            {
                cnt++;
                i = i + 2;
            
              
            // Current three consecutive
            // characters are not same
            else 
            {
                i++;
            }
        }
        return cnt;
    }
  
    // Driver code
    static public void main(String[] arg) 
    {
        String str = "aabbbcc";
        int n = str.length();
  
        System.out.println(getCount(str.toCharArray(), n));
    }
}
  
// This code is contributed by PrinciRaj1992

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Python3

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# Python3 implementation of the approach
  
# Function to return the count of characters
# that are to be inserted in str1 such that no
# three consecutive characters are same
def getCount(str1, n):
  
    # To store the count of
    # operations required
    cnt = 0;
  
    i = 0;
    while (i < n - 2):
  
        # A character needs to be
        # inserted after str1[i + 1]
        if (str1[i] == str1[i + 1] and 
            str1[i] == str1[i + 2]):
            cnt += 1
            i = i + 2
  
        # Current three consecutive
        # characters are not same
        else:
            i += 1
  
    return cnt
  
# Driver code
str1 = "aabbbcc"
n = len(str1)
  
print(getCount(str1, n))
  
# This code is contributed by Mohit Kumar 

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C#

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// C# implementation of the above approach
using System;
  
class GFG
{
      
    // Function to return the count of characters 
    // that are to be inserted in str such that no 
    // three consecutive characters are same 
    static int getCount(string str, int n) 
    
  
        // To store the count of 
        // operations required 
        int cnt = 0; 
  
        int i = 0; 
        while (i < n - 2) 
        
  
            // A character needs to be 
            // inserted after str[i + 1] 
            if (str[i] == str[i + 1] && 
                str[i] == str[i + 2]) 
            
                cnt++; 
                i = i + 2; 
            
              
            // Current three consecutive 
            // characters are not same 
            else
            
                i++; 
            
        
        return cnt; 
    
  
    // Driver code 
    static public void Main () 
    
        string str = "aabbbcc"
        int n = str.Length; 
  
        Console.WriteLine(getCount(str, n)); 
    
}
  
// This code is contributed by AnkitRai01

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Output:

1


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