Generate a string of size N whose each substring of size M has exactly K distinct characters

Last Updated : 31 Oct, 2023

Given 3 positive integers N, M, and K. the task is to construct a string of length N consisting of lowercase letters such that each substring of length M having exactly K distinct letters.
Examples:

Input: N = 5, M = 2, K = 2
Output: abade
Explanation:
Each substring of size 2 “ab”, “ba”, “ad”, “de” have 2 distinct letters.
Input: N = 7, M = 5, K = 3
Output: abcaaab
Explanation:
Each substring of size 5 “tleel”, “leelt”, “eelte” have 3 distinct letters.

Approach: In a string of size N, every substring of size M must contain exactly K distinct letters-

Construct a string having K distinct alphabets starting from ‘a’ to ‘z’ up to the size of M and put the rest of letters like ‘a’..
Since we have generated a string of size M with K distinct value. Now, keep repeating it till we reach string size of N.

Below is the implementation of the above approach:

C++

   // C++ program to generate a string of size N
// whose each substring of size M
// has exactly K distinct characters
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to generate the string
string generateString(int N, int M, int K)
{
 
    // Declare empty string
    string s = "";
 
    // counter for M
    int cnt1 = 0;
 
    // counter for K
    int cnt2 = 0;
 
    // Loop to generate string size of N
    for (int i = 0; i < N; i++) {
        cnt1++;
        cnt2++;
 
        // Generating K distinct
        // letters one by one
        if (cnt1 <= M) {
            if (cnt2 <= K) {
                s = s + char(96 + cnt1);
            }
 
            // After generating b distinct letters,
            // append rest a-b letters as 'a'
            else {
                s = s + 'a';
            }
        }
 
        // Reset the counter value
        // and repeat the process
        else {
            cnt1 = 1;
            cnt2 = 1;
            s = s + 'a';
        }
    }
 
    // return final result string
    return s;
}
 
// Driver code
int main()
{
    int N = 7, M = 5, K = 3;
 
    cout << generateString(N, M, K) << endl;
 
    return 0;
}
 
  

Java

   // Java program to generate a String of size N 
// whose each subString of size M 
// has exactly K distinct characters 
import java.util.*;
class GFG{ 
 
// Function to generate the String 
static String generateString(int N, int M, int K) 
{ 
 
    // Declare empty String 
    String s = ""; 
 
    // counter for M 
    int cnt1 = 0; 
 
    // counter for K 
    int cnt2 = 0; 
 
    // Loop to generate String size of N 
    for (int i = 0; i < N; i++) 
    { 
        cnt1++; 
        cnt2++; 
 
        // Generating K distinct 
        // letters one by one 
        if (cnt1 <= M) 
        { 
            if (cnt2 <= K) 
            { 
                s = s + (char)(96 + cnt1); 
            } 
 
            // After generating b distinct letters, 
            // append rest a-b letters as 'a' 
            else
            { 
                s = s + 'a'; 
            } 
        } 
 
        // Reset the counter value 
        // and repeat the process 
        else
        { 
            cnt1 = 1; 
            cnt2 = 1; 
            s = s + 'a'; 
        } 
    } 
 
    // return final result String 
    return s; 
} 
 
// Driver code 
public static void main(String[] args) 
{ 
    int N = 7, M = 5, K = 3; 
 
    System.out.println(generateString(N, M, K)); 
}
} 
 
// This code is contributed by 29AjayKumar
 
  

Python3

   # Python3 program to generate a string of size N
# whose each substring of size M
# has exactly K distinct characters
# Function to generate the string
def generateString(N, M, K):
 
    # Declare empty string
    s = ""
 
    # counter for M
    cnt1 = 0
 
    # counter for K
    cnt2 = 0
 
    # Loop to generate string size of N
    for i in range (N):
        cnt1 += 1
        cnt2 += 1
 
        # Generating K distinct
        # letters one by one
        if (cnt1 <= M):
            if (cnt2 <= K):
                s = s + chr(96 + cnt1)
             
            # After generating b distinct letters,
            # append rest a-b letters as 'a'
            else:
                s = s + 'a'
 
        # Reset the counter value
        # and repeat the process
        else:
            cnt1 = 1
            cnt2 = 1
            s = s + 'a'
 
    # return final result string
    return s
 
# Driver code
if __name__ == "__main__":  
    N = 7
    M = 5
    K = 3
    print (generateString(N, M, K))
     
# This code is contributed by Chitranayal
 
  

C#

   // C# program to generate a String of 
// size N whose each subString of size 
// M has exactly K distinct characters 
using System;
 
class GFG{ 
 
// Function to generate the String 
static String generateString(int N, int M, int K) 
{ 
 
    // Declare empty String 
    String s = ""; 
 
    // Counter for M 
    int cnt1 = 0; 
 
    // Counter for K 
    int cnt2 = 0; 
 
    // Loop to generate String size of N 
    for(int i = 0; i < N; i++) 
    { 
       cnt1++; 
       cnt2++; 
        
       // Generating K distinct 
       // letters one by one 
       if (cnt1 <= M) 
       { 
           if (cnt2 <= K) 
           { 
               s = s + (char)(96 + cnt1); 
           } 
            
           // After generating b distinct letters, 
           // append rest a-b letters as 'a' 
           else
           { 
               s = s + 'a'; 
           } 
       } 
        
       // Reset the counter value 
       // and repeat the process 
       else
       { 
           cnt1 = 1; 
           cnt2 = 1; 
           s = s + 'a'; 
       } 
    } 
     
    // Return readonly result String 
    return s; 
} 
 
// Driver code 
public static void Main(String[] args) 
{ 
    int N = 7, M = 5, K = 3; 
 
    Console.WriteLine(generateString(N, M, K)); 
}
} 
 
// This code is contributed by Rajput-Ji
 
  

Javascript

   <script>
 
// Javascript program to generate
// a String of size N
// whose each subString of size M
// has exactly K distinct characters
 
    // Function to generate the String
    function generateString(N,M,K)
    {
        // Declare empty string
    let s = "";
  
    // counter for M
    let cnt1 = 0;
  
    // counter for K
    let cnt2 = 0;
  
    // Loop to generate string size of N
    for (let i = 0; i < N; i++) {
        cnt1++;
        cnt2++;
  
        // Generating K distinct
        // letters one by one
        if (cnt1 <= M) {
            if (cnt2 <= K) {
                s = s + String.fromCharCode(96 + cnt1);
            }
  
            // After generating b distinct letters,
            // append rest a-b letters as 'a'
            else {
                s = s + 'a';
            }
        }
  
        // Reset the counter value
        // and repeat the process
        else {
            cnt1 = 1;
            cnt2 = 1;
            s = s + 'a';
        }
    }
  
    // return final result string
    return s;
    }
     
    // Driver code
    let N = 7, M = 5, K = 3;
    document.write( generateString(N, M, K))
     
     
    // This code is contributed
    // by avanitrachhadiya2155
     
</script>
 
  

Output

abcaaab

Time complexity: O(N)
Space complexity: O(1)

Count number of substrings of a string consisting of same characters

divyeshrabadiya07

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Practice Tags :

Generate a string of size N whose each substring of size M has exactly K distinct characters

C++

Java

Python3

C#

Javascript

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