Data Modelling & AI Data Structure & Algorithm

Maximum subarray sum in array formed by repeating the given array k times

23 June 2025

0

Given an integer k and an integer array arr[] of n elements, the task is to find the largest sub-array sum in the modified array (formed by repeating the given array k times). For example, if arr[] = {1, 2} and k = 3 then the modified array will be {1, 2, 1, 2, 1, 2}.

Examples:

Input: arr[] = {1, 2}, k = 3
Output: 9
Modified array will be {1, 2, 1, 2, 1, 2}
And the maximum sub-array sum will be 1 + 2 + 1 + 2 + 1 + 2 = 9

Input: arr[] = {1, -2, 1}, k = 5
Output: 2

A simple solution is to create an array of size n * k, then run Kadane’s algorithm to find the maximum sub-array sum.

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to return the maximum
// subarray sum of arr[]
long maxSubArrSum(vector<int>& a, int len)
{
    int size = len;
    int max_so_far = INT_MIN;
    long max_ending_here = 0;
 
    for (int i = 0; i < size; i++) {
        max_ending_here = max_ending_here + a[i];
        if (max_so_far < max_ending_here)
            max_so_far = max_ending_here;
        if (max_ending_here < 0)
            max_ending_here = 0;
    }
    return max_so_far;
}
 
// Function to return the maximum sub-array
// sum of the modified array
long maxSubKSum(vector<int>& arr, int k, int len)
{
    vector<int> res;
 
    while (k--) {
        for (int i = 0; i < len; i++) {
            res.push_back(arr[i]);
        }
    }
 
    return maxSubArrSum(res, res.size());
}
 
// Driver code
int main()
{
    vector<int> arr = { 1, 2 };
    int arrlen = arr.size();
    int k = 3;
    cout << maxSubKSum(arr, k, arrlen) << endl;
    return 0;
}

Java

import java.util.*;
import java.io.*;
import java.util.List;
 
public class Gfg {
    // Function to return the maximum subarray sum of arr[]
    public static long maxSubArrSum(List<Integer> a,
                                    int len)
    {
        int size = len;
        long maxSoFar = Integer.MIN_VALUE;
        long maxEndingHere = 0;
 
        for (int i = 0; i < size; i++) {
            maxEndingHere = maxEndingHere + a.get(i);
            if (maxSoFar < maxEndingHere)
                maxSoFar = maxEndingHere;
            if (maxEndingHere < 0)
                maxEndingHere = 0;
        }
        return maxSoFar;
    }
 
    // Function to return the maximum sub-array sum of the
    // modified array
    public static long maxSubKSum(List<Integer> arr, int k,
                                  int len)
    {
        List<Integer> res = new ArrayList<>();
 
        while (k-- > 0) {
            for (int i = 0; i < len; i++) {
                res.add(arr.get(i));
            }
        }
 
        return maxSubArrSum(res, res.size());
    }
 
    // Driver code
    public static void main(String[] args)
    {
        List<Integer> arr = Arrays.asList(1, 2);
        int arrlen = arr.size();
        int k = 3;
        System.out.println(maxSubKSum(arr, k, arrlen));
    }
}

C#

using System;
using System.Collections.Generic;
 
class Gfg {
 
  // Function to return the maximum subarray sum of arr[]
  public static long maxSubArrSum(List<int> a, int len)
  {
    int size = len;
    long maxSoFar = int.MinValue;
    long maxEndingHere = 0;
    for (int i = 0; i < size; i++) {
      maxEndingHere = maxEndingHere + a[i];
      if (maxSoFar < maxEndingHere)
        maxSoFar = maxEndingHere;
      if (maxEndingHere < 0)
        maxEndingHere = 0;
    }
    return maxSoFar;
  }
 
  // Function to return the maximum sub-array
  // sum of the modified array
  public static long maxSubKSum(List<int> arr, int k,
                                int len)
  {
    List<int> res = new List<int>();
    while (k-- > 0) {
      for (int i = 0; i < len; i++) {
        res.Add(arr[i]);
      }
    }
    return maxSubArrSum(res, res.Count);
  }
 
  // Driver code
  public static void Main(string[] args)
  {
    List<int> arr = new List<int>() { 1, 2 };
    int arrlen = arr.Count;
    int k = 3;
    Console.WriteLine(maxSubKSum(arr, k, arrlen));
  }
}

Javascript

// Javascript implementation of the approach
 
// Function to return the maximum
// subarray sum of arr[]
function maxSubArrSum(a, len)
{
    let size = len;
    let max_so_far = Number.MIN_SAFE_INTEGER;
    let max_ending_here = 0;
 
    for (let i = 0; i < size; i++) {
        max_ending_here = max_ending_here + a[i];
        if (max_so_far < max_ending_here)
            max_so_far = max_ending_here;
        if (max_ending_here < 0)
            max_ending_here = 0;
    }
    return max_so_far;
}
 
// Function to return the maximum sub-array
// sum of the modified array
function maxSubKSum(arr, k, len)
{
    let res=[];
 
    while (k--) {
        for (let i = 0; i < len; i++) {
            res.push(arr[i]);
        }
    }
 
    return maxSubArrSum(res, res.length);
}
 
// Driver code
let arr = [ 1, 2 ];
let arrlen = arr.length;
let k = 3;
console.log(maxSubKSum(arr, k, arrlen));

Python3

# Python implementation of the approach
 
# Import the sys module to handle the max size of an integer
import sys
 
def maxSubArrSum(a, len):
    """
    Returns the maximum subarray sum of arr[]
     
    Arguments:
    a -- list of integers
    len -- length of the list
     
    Returns:
    long -- maximum subarray sum
    """
    size = len
    max_so_far = -sys.maxsize-1
    max_ending_here = 0
 
    for i in range(size):
        max_ending_here += a[i]
        if max_so_far < max_ending_here:
            max_so_far = max_ending_here
        if max_ending_here < 0:
            max_ending_here = 0
    return max_so_far
 
def maxSubKSum(arr, k, len):
    """
    Returns the maximum sub-array sum of the modified array
     
    Arguments:
    arr -- list of integers
    k -- number of times the array is repeated
    len -- length of the original array
     
    Returns:
    long -- maximum sub-array sum of the modified array
    """
    res = []
 
    for i in range(k):
        for j in range(len):
            res.append(arr[j])
 
    return maxSubArrSum(res, len * k)
 
if __name__ == "__main__":
    arr = [1, 2]
    arrlen = len(arr)
    k = 3
    print(maxSubKSum(arr, k, arrlen))

Output

Time Complexity: O(n * k)
Auxiliary Space: O(n * k)

A better solution is to calculate the sum of the array arr[] and store it in sum.

If sum < 0 then calculate the maximum sub-array sum of an array formed by concatenating the array two times irrespective of the K. For example, take arr[] = {1, -4, 1} and k = 5. The sum of the array is less than 0. So, the maximum sub-array sum of the array can be found after concatenating the array two times only irrespective of the value of K i.e. b[] = {1, -4, 1, 1, -4, 1} and the maximum sub-array sum = 1 + 1 = 2
If sum > 0 then maximum sub-array will include the maximum sum as calculated in the previous step (where the array was concatenated twice) + the rest (k – 2) repetitions of the array can also be included as their sum is greater than 0 that will contribute to the maximum sum.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach
#include<bits/stdc++.h>
using namespace std;
 
    // Function to concatenate array
    void arrayConcatenate(int *arr, int *b,
                                int k,int len)
    {
        // Array b will be formed by concatenation
        // array a exactly k times
        int j = 0;
        while (k > 0) 
        {
 
            for (int i = 0; i < len; i++)
            {
                b[j++] = arr[i];
            }
            k--;
        }
    }
 
    // Function to return the maximum 
    // subarray sum of arr[]
    long maxSubArrSum(int *a,int len)
    {
        int size = len;
        int max_so_far = INT_MIN;
        long max_ending_here = 0;
 
        for (int i = 0; i < size; i++)
        {
            max_ending_here = max_ending_here + a[i];
            if (max_so_far < max_ending_here)
                max_so_far = max_ending_here;
            if (max_ending_here < 0)
                max_ending_here = 0;
        }
        return max_so_far;
    }
 
    // Function to return the maximum sub-array 
    // sum of the modified array
    long maxSubKSum(int *arr, int k,int len)
    {
        int arrSum = 0;
        long maxSubArrSum1 = 0;
 
        int b[(2 * len)]={0};
 
        // Concatenating the array 2 times
        arrayConcatenate(arr, b, 2,len);
 
        // Finding the sum of the array
        for (int i = 0; i < len; i++)
            arrSum += arr[i];
 
        // If sum is less than zero
        if (arrSum < 0)
            maxSubArrSum1 = maxSubArrSum(b,2*len);
 
        // If sum is greater than zero
        else
            maxSubArrSum1 = maxSubArrSum(b,2*len) +
                        (k - 2) * arrSum;
 
        return maxSubArrSum1;
    }
 
    // Driver code
    int main()
    {
        int arr[] = { 1, -2, 1 };
        int arrlen=sizeof(arr)/sizeof(arr[0]);
        int k = 5;
        cout << maxSubKSum(arr, k,arrlen) << endl;
        return 0;
    }
     
// This code is contributed by mits

Java

// Java implementation of the approach
public class GFG {
 
    // Function to concatenate array
    static void arrayConcatenate(int arr[], int b[], 
                                             int k)
    {
        // Array b will be formed by concatenation
        // array a exactly k times
        int j = 0;
        while (k > 0) {
 
            for (int i = 0; i < arr.length; i++) {
                b[j++] = arr[i];
            }
            k--;
        }
    }
 
    // Function to return the maximum 
    // subarray sum of arr[]
    static int maxSubArrSum(int a[])
    {
        int size = a.length;
        int max_so_far = Integer.MIN_VALUE,
            max_ending_here = 0;
 
        for (int i = 0; i < size; i++) {
            max_ending_here = max_ending_here + a[i];
            if (max_so_far < max_ending_here)
                max_so_far = max_ending_here;
            if (max_ending_here < 0)
                max_ending_here = 0;
        }
        return max_so_far;
    }
 
    // Function to return the maximum sub-array 
    // sum of the modified array
    static long maxSubKSum(int arr[], int k)
    {
        int arrSum = 0;
        long maxSubArrSum = 0;
 
        int b[] = new int[(2 * arr.length)];
 
        // Concatenating the array 2 times
        arrayConcatenate(arr, b, 2);
 
        // Finding the sum of the array
        for (int i = 0; i < arr.length; i++)
            arrSum += arr[i];
 
        // If sum is less than zero
        if (arrSum < 0)
            maxSubArrSum = maxSubArrSum(b);
 
        // If sum is greater than zero
        else
            maxSubArrSum = maxSubArrSum(b) +
                          (k - 2) * arrSum;
 
        return maxSubArrSum;
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, -2, 1 };
        int k = 5;
        System.out.println(maxSubKSum(arr, k));
    }
}

Python3

# Python approach to this problem
 
# A python module where element 
# are added to list k times
def MaxsumArrKtimes(c, ktimes):
     
    # Store element in list d k times
    d = c * ktimes
     
    # two variable which can keep 
    # track of maximum sum seen
    # so far and maximum sum ended.
    maxsofar = -99999
    maxending = 0
     
    for i in d:
        maxending = maxending + i
        if maxsofar < maxending:
            maxsofar = maxending
        if maxending < 0:
            maxending = 0
    return maxsofar
     
# Get the Maximum sum of element
print(MaxsumArrKtimes([1, -2, 1], 5))
     
# This code is contributed by AnupGaurav.
       

C#

// C# implementation of the approach 
using System;
 
class GFG 
{ 
 
// Function to concatenate array 
static void arrayConcatenate(int []arr, 
                             int []b, int k) 
{ 
    // Array b will be formed by concatenation 
    // array a exactly k times 
    int j = 0; 
    while (k > 0)
    { 
        for (int i = 0; i < arr.Length; i++) 
        { 
            b[j++] = arr[i]; 
        } 
        k--; 
    } 
} 
 
// Function to return the maximum 
// subarray sum of arr[] 
static int maxSubArrSum(int []a) 
{ 
    int size = a.Length; 
    int max_so_far = int.MinValue, 
        max_ending_here = 0; 
 
    for (int i = 0; i < size; i++) 
    { 
        max_ending_here = max_ending_here + a[i]; 
        if (max_so_far < max_ending_here) 
            max_so_far = max_ending_here; 
        if (max_ending_here < 0) 
            max_ending_here = 0; 
    } 
    return max_so_far; 
} 
 
// Function to return the maximum sub-array 
// sum of the modified array 
static long maxSubKSum(int []arr, int k) 
{ 
    int arrSum = 0; 
    long maxSubArrsum = 0; 
 
    int []b = new int[(2 * arr.Length)]; 
 
    // Concatenating the array 2 times 
    arrayConcatenate(arr, b, 2); 
 
    // Finding the sum of the array 
    for (int i = 0; i < arr.Length; i++) 
        arrSum += arr[i]; 
 
    // If sum is less than zero 
    if (arrSum < 0) 
        maxSubArrsum = maxSubArrSum(b); 
 
    // If sum is greater than zero 
    else
        maxSubArrsum = maxSubArrSum(b) + 
                       (k - 2) * arrSum; 
 
    return maxSubArrsum; 
} 
 
// Driver code 
public static void Main() 
{ 
    int []arr = { 1, -2, 1 }; 
    int k = 5; 
    Console.WriteLine(maxSubKSum(arr, k)); 
} 
} 
 
// This code is contributed by Ryuga

PHP

<?php 
 
// PHP implementation of the approach
 
// Function to concatenate array
function arrayConcatenate(&$arr, &$b, $k)
{
    // Array b will be formed by concatenation
    // array a exactly k times
    $j = 0;
    while ($k > 0) 
    {
 
        for ($i = 0; $i < sizeof($arr); $i++) 
        {
            $b[$j++] = $arr[$i];
        }
        $k--;
    }
}
 
// Function to return the maximum 
// subarray sum of arr[]
function maxSubArrSum(&$a)
{
    $size = sizeof($a);
    $max_so_far = 0;
    $max_ending_here = 0;
 
    for ($i = 0; $i < $size; $i++) 
    {
        $max_ending_here = $max_ending_here + $a[$i];
        if ($max_so_far < $max_ending_here)
            $max_so_far = $max_ending_here;
        if ($max_ending_here < 0)
            $max_ending_here = 0;
    }
    return $max_so_far;
}
 
// Function to return the maximum sub-array 
// sum of the modified array
function maxSubKSum(&$arr,$k)
{
    $arrSum = 0;
    $maxSubArrSum = 0;
 
    $b = array_fill(0,(2 * sizeof($arr)),NULL);
 
    // Concatenating the array 2 times
    arrayConcatenate($arr, $b, 2);
 
    // Finding the sum of the array
    for ($i = 0; $i < sizeof($arr); $i++)
        $arrSum += $arr[$i];
 
    // If sum is less than zero
    if ($arrSum < 0)
        $maxSubArrSum = maxSubArrSum($b);
 
    // If sum is greater than zero
    else
        $maxSubArrSum = maxSubArrSum($b) +
                    ($k - 2) * $arrSum;
 
    return $maxSubArrSum;
}
 
    // Driver code
    $arr = array(1, -2, 1 );
    $k = 5;
    echo maxSubKSum($arr, $k);
     
// This code is contributed by Ita_c.    
?>

Javascript

<script>
// Javascript implementation of the approach
 
// Function to concatenate array
function arrayConcatenate(arr,b,k)
{
    // Array b will be formed by concatenation
        // array a exactly k times
        let j = 0;
        while (k > 0) {
   
            for (let i = 0; i < arr.length; i++) {
                b[j++] = arr[i];
            }
            k--;
        }
}
 
// Function to return the maximum 
    // subarray sum of arr[]
function maxSubArrSum(a)
{
    let size = a.length;
        let max_so_far = Number.MIN_VALUE,
            max_ending_here = 0;
   
        for (let i = 0; i < size; i++) {
            max_ending_here = max_ending_here + a[i];
            if (max_so_far < max_ending_here)
                max_so_far = max_ending_here;
            if (max_ending_here < 0)
                max_ending_here = 0;
        }
        return max_so_far;
}
 
// Function to return the maximum sub-array 
    // sum of the modified array
function maxSubKSum(arr,k)
{
    let arrSum = 0;
        let maxsubArrSum = 0;
   
        let b = new Array(2 * arr.length);
   
        // Concatenating the array 2 times
        arrayConcatenate(arr, b, 2);
   
        // Finding the sum of the array
        for (let i = 0; i < arr.length; i++)
            arrSum += arr[i];
   
        // If sum is less than zero
        if (arrSum < 0)
            maxsubArrSum = maxSubArrSum(b);
   
        // If sum is greater than zero
        else
            maxsubArrSum = maxSubArrSum(b) +
                          (k - 2) * arrSum;
   
        return maxsubArrSum;
}
 
 // Driver code
let arr=[ 1, -2, 1 ];
let k = 5;
document.write(maxSubKSum(arr, k));
 
 
// This code is contributed by rag2127
</script>

Output

Complexity Analysis:

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

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Maximum subarray sum in array formed by repeating the given array k times

C++

Java

C#

Javascript

Python3

C++

Java

Python3

C#

PHP

Javascript

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