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Generate Array whose sum of all K-size subarrays divided by N leaves remainder X
  • Last Updated : 02 Jul, 2020

Given three integer N, K and X, the task is to create an array of length N suach that sum of all its K-length subarrays modulo N is X.

Examples:

Input: N = 6, K = 3, X = 3
Output: 9 6 6 9 6 6
Explanation:
All subarrays of length 3 and their respective sum%N values are as follows:
[9, 6, 6] Sum = 21 % 6 = 3
[6, 6, 9] sum = 21 % 6 = 3
[6, 9, 6] sum = 21 % 6 = 3
[9, 6, 6] sum = 21 % 6 = 3
Since all its subarrays have sum % N = X (=3), the generated array is valid.

Input: N = 4, K = 2, X = 2
Output: 6 4 6 4

Approach:
We can observe that in order to make the sum of any subarray of size K modulo N to be equal to X, the subarray needs to have a K – 1 elements equal to N and 1 element equal to N + X.



Illustration:

If N = 6, K = 3, X = 3
Here a K length subarray needs to be a permutation of {9, 6, 6} where 2 (K – 1) elements are divisible by 6 and 1 element has modulo N equal to X( 9%6 = 3)
Sum of subarray % N = (21 % 6) = 3 (same as X)
Hence, each K length

Hence, follow the steps below to solve the problem:

  • Iterate i from 0 to N – 1, to print the ith element of the required subarray.
  • If i % K is equal to 0, print N + X. Otherwise, for all other values of i, print N.
  • This ensures that every possible K-length subarray has a sum K*N + X. Hence sum modulo N is X for all such subarrays.

Below is the implementation of the above approach.

C++

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// C++ implementation of the
// above approach
#include <bits/stdc++.h>
using namespace std;
  
// Funtion prints the required array
void createArray(int n, int k, int x)
{
    for (int i = 0; i < n; i++) {
        // First element of each K
        // length subarrays
        if (i % k == 0) {
            cout << x + n << " ";
        }
        else {
            cout << n << " ";
        }
    }
}
  
// Driver Program
int main()
{
  
    int N = 6, K = 3, X = 3;
    createArray(N, K, X);
}

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Java

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// Java implementation of the above approach
import java.util.*;
class GFG{
  
// Function prints the required array
static void createArray(int n, int k, int x)
{
    for(int i = 0; i < n; i++)
    {
          
       // First element of each K
       // length subarrays
       if (i % k == 0
       {
           System.out.print((x + n) + " ");
       }
       else
       {
           System.out.print(n + " ");
       }
    }
}
  
// Driver Code
public static void main(String args[])
{
    int N = 6, K = 3, X = 3;
      
    createArray(N, K, X);
}
}
  
// This code is contributed by Code_Mech

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Python3

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# Python3 implementation of the 
# above approach 
  
# Funtion prints the required array 
def createArray(n, k, x):
      
    for i in range(n):
          
        # First element of each K
        # length subarrays
        if (i % k == 0):
            print(x + n, end = " ")
        else :
            print(n, end = " ")
  
# Driver code
N = 6
K = 3
X = 3
  
createArray(N, K, X)
  
# This code is contributed by Vishal Maurya.

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C#

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// C# implementation of the above approach
using System;
class GFG{
  
// Function prints the required array
static void createArray(int n, int k, int x)
{
    for(int i = 0; i < n; i++)
    {
         
       // First element of each K
       // length subarrays
       if (i % k == 0) 
       {
           Console.Write((x + n) + " ");
       }
       else
       {
           Console.Write(n + " ");
       }
    }
}
  
// Driver Code
public static void Main()
{
    int N = 6, K = 3, X = 3;
      
    createArray(N, K, X);
}
}
  
// This code is contributed by Code_Mech

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Output:

9 6 6 9 6 6

Time Complexity: O(N)
Auxiliary Space: O(1)

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