Maximum count of sub-strings of length K consisting of same characters

Given a string str and an integer k. The task is to count the occurrences of sub-strings of length k that consist of the same characters. There can be multiple such sub-strings possible of length k, choose the count of the one which appears the maximum number of times as the sub-string (non-overlapping) of str.

Examples:

Input: str = “aaacaabbaa”, k = 2
Output: 3
“aa” and “bb” are the only sub-strings of length 2 that consist of the same characters.
“bb” appears only once as a sub-string of str whereas “aa” appears thrice (which is the answer)

Input: str = “abab”, k = 2
Output: 0

Approach: Iterate over all the characters from ‘a’ to ‘z’ and count the number of times a string of length k consisting only of the current character appears as a sub-string of str. Print the maximum of these counts in the end.



Below is the implementation of the above approach:

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the count
// of the required sub-strings
int maxSubStrings(string s, int k)
{
    int maxSubStr = 0, n = s.size();
  
    // Iterate over all characters
    for (int c = 0; c < 26; c++) {
        char ch = 'a' + c;
  
        // Count with current character
        int curr = 0;
        for (int i = 0; i <= n - k; i++) {
            if (s[i] != ch)
                continue;
            int cnt = 0;
            while (i < n && s[i] == ch && cnt != k) {
                i++;
                cnt++;
            }
            i--;
  
            // If the substring has a length k
            // then increment count with current character
            if (cnt == k)
                curr++;
        }
  
        // Update max count
        maxSubStr = max(maxSubStr, curr);
    }
    return maxSubStr;
}
  
// Driver Code
int main()
{
    string s = "aaacaabbaa";
    int k = 2;
    cout << maxSubStrings(s, k);
  
    return 0;
}
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java implementation of the approach
import java.util.*;
import java.lang.*;
import java.io.*;
  
class GFG
{
      
// Function to return the count
// of the required sub-strings
static int maxSubStrings(String s, int k)
{
    int maxSubStr = 0, n = s.length();
  
    // Iterate over all characters
    for (int c = 0; c < 26; c++) 
    {
        char ch = (char)((int)'a' + c);
  
        // Count with current character
        int curr = 0;
        for (int i = 0; i <= n - k; i++) 
        {
            if (s.charAt(i) != ch)
                continue;
            int cnt = 0;
            while (i < n && s.charAt(i) == ch &&
                                        cnt != k) 
            {
                i++;
                cnt++;
            }
            i--;
  
            // If the substring has a length
            //  k then increment count with 
            // current character
            if (cnt == k)
                curr++;
        }
  
        // Update max count
        maxSubStr = Math.max(maxSubStr, curr);
    }
    return maxSubStr;
}
  
// Driver Code
public static void main(String []args)
{
    String s = "aaacaabbaa";
    int k = 2;
    System.out.println(maxSubStrings(s, k));
}
}
  
// This code is contributed by 
// tufan_gupta2000
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python 3 implementation of the approach
  
# Function to return the count
# of the required sub-strings
def maxSubStrings(s, k):
    maxSubStr = 0
    n = len(s)
  
    # Iterate over all characters
    for c in range(27):
        ch = chr(ord('a') + c)
  
        # Count with current character
        curr = 0
        for i in range(n - k):
            if (s[i] != ch):
                continue
            cnt = 0
            while (i < n and s[i] == ch and 
                                   cnt != k):
                i += 1
                cnt += 1
      
            i -= 1
  
            # If the substring has a length k then
            # increment count with current character
            if (cnt == k):
                curr += 1
  
        # Update max count
        maxSubStr = max(maxSubStr, curr)
  
    return maxSubStr
  
# Driver Code
if __name__ == '__main__':
    s = "aaacaabbaa"
    k = 2
    print(maxSubStrings(s, k))
  
# This code is contributed by
# Surendra_Gangwar
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# implementation of the approach 
using System;
  
class GFG 
          
    // Function to return the count 
    // of the required sub-strings 
    static int maxSubStrings(String s, int k) 
    
        int maxSubStr = 0, n = s.Length; 
      
        // Iterate over all characters 
        for (int c = 0; c < 26; c++) 
        
            char ch = (char)((int)'a' + c); 
      
            // Count with current character 
            int curr = 0; 
            for (int i = 0; i <= n - k; i++) 
            
                if (s[i] != ch) 
                    continue
                int cnt = 0; 
                while (i < n && s[i] == ch && 
                                cnt != k) 
                
                    i++; 
                    cnt++; 
                
                i--; 
      
                // If the substring has a length 
                // k then increment count with 
                // current character 
                if (cnt == k) 
                    curr++; 
            
      
            // Update max count 
            maxSubStr = Math.Max(maxSubStr, curr); 
        
        return maxSubStr; 
    
      
    // Driver Code 
    public static void Main() 
    
        string s = "aaacaabbaa"
        int k = 2; 
        Console.WriteLine(maxSubStrings(s, k)); 
    
}
  
// This code is contributed by Ryuga
chevron_right

Output:
3

Time Complexity: O(n), where n is the length of the string.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.




Recommended Posts:


Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Article Tags :
Practice Tags :