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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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:

C++

// 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; 
} 

Java

// 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 

Python3

# 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 

C#

// 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 

Output:

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

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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