Find maximum sum array of length less than or equal to m

Difficulty Level : Hard
Last Updated : 24 Aug, 2020

Given n arrays of different length consisting of integers, the target is to pick atmost one subarray from an array such that the combined length of all picked subarrays does not become greater than m and also sum of their elements is maximum.(also given that value of n can not be more than 100)

Prerequisite : Knapsack Problem

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Examples :

Input :
n = 5, m = 6
arr[][m] = {{3, 2, 3, 5},
            {2, 7, -1},
            {2, 8, 10},
            {4, 5, 2, 6, 1},
            {3, 2, 3, -2}};
Output : Maximum sum can be obtained is 39
Explanation : We are allowed to pick at most
one subarray from every array. 
We get total sum 39 as ((5) + (7) + (8 + 10) + 
(4 + 5))

Input :
n = 3, m = 4
arr[][m] = {{2, 3, 2},  
            {3, -1, 7, 10},
            {4, 8, 10, -5, 3}};
Output : Maximum sum can be obtained is 35

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

This problem is similar to Knapsack problem.where you have to either pick an element or leave it. We will have the same strategy here.
Given that the total number of elements in these n arrays is atmost 10^5. It is also known that m is atmost 10^3 and the input arrays can contain negative numbers. First, make a DP table (2D array) of size n * m and then, pre-compute the cumulative sum of an array so that maximum sum of every length from 1 to n of that array can be easily computed, so that for every given array there can be a maximum contiguous sum for length k, where k is from 1 to length of the array.
In detail, process input arrays one by one. First, compute the maximum sum subarrays of processed array for all sizes from 1 to length. Then, update our dynamic programming table with these values and we start processing the next array.

Algorithm :

Pick one array from n arrays and start processing it.
Calculate maximum contiguous sum for length k, k is from 1 to length of the array and save it in the array maxSum.
Now, fill the DP table by storing maximum sum possible for every length 0 to m.

In the last step we traverse last row(nth row) of DP table and pick maximum sum possible and return it.

Below is the implementation of above approach :

C++

// A Dynamic Programming based C++ program to find 
// maximum sum of array of size less than or 
// equal to m from given n arrays 
#include <bits/stdc++.h> 
using namespace std; 
  
/* N and M to define sizes of arr, 
dp, current_arr and maxSum */
#define N 105 
#define M 1001 
  
// INF to define min value 
#define INF -1111111111 
  
// Function to find maximum sum 
int maxSum(int arr[][N]) 
{ 
    // dp array of size N x M 
    int dp[N][M]; 
  
    // current_arr of size M 
    int current_arr[M]; 
  
    // maxsum of size M 
    int maxsum[M]; 
  
    memset(dp, -1, sizeof(dp[0][0]) * N * M); 
  
    current_arr[0] = 0; 
  
    // if we have 0 elements 
    // from 0th array 
    dp[0][0] = 0; 
  
    for (int i = 1; i <= 5; i++) { 
        int len = arr[i - 1][0]; 
  
        // compute the cumulative sum array 
        for (int j = 1; j <= len; j++) { 
            current_arr[j] = arr[i - 1][j]; 
            current_arr[j] += current_arr[j - 1]; 
            maxsum[j] = INF; 
        } 
  
        // calculating the maximum contiguous 
        // array for every length j, j is from 
        // 1 to lengtn of the array 
        for (int j = 1; j <= len && j <= 6; j++) 
            for (int k = 1; k <= len; k++) 
                if (j + k - 1 <= len) 
                    maxsum[j] = max(maxsum[j], 
                                current_arr[j + k - 1] - 
                                current_arr[k - 1]); 
  
        // every state is depending on 
        // its previous state 
        for (int j = 0; j <= 6; j++) 
            dp[i][j] = dp[i - 1][j]; 
  
        // computation of dp table similar 
        // approach as knapsack problem 
        for (int j = 1; j <= 6; j++) 
            for (int cur = 1; cur <= j && cur <= len; cur++) 
                dp[i][j] = max(dp[i][j], 
                            dp[i - 1][j - cur] + 
                                        maxsum[cur]); 
    } 
  
    // now we have done processing with 
    // the last array lets find out 
    // what is the maximum sum possible 
    int ans = 0; 
    for (int i = 0; i <= 6; i++) 
        ans = max(ans, dp[5][i]);     
  
    return ans; 
} 
  
// Driver program 
int main() 
{ 
    // first element of each 
    // row is the size of that row 
    int arr[][N] = { { 3, 2, 3, 5 }, 
                    { 2, 7, -1 }, 
                    { 2, 8, 10 }, 
                    { 4, 5, 2, 6, 1 }, 
                    { 3, 2, 3, -2 } }; 
  
    cout << "Maximum sum can be obtained "
        << "is : " << maxSum(arr) << "\n"; 
} 

Java

// Java program to find maximum sum 
// of array of size less than or 
// equal to m from given n arrays 
import java.io.*; 
  
public class GFG 
{ 
    /* N and M to define 
    sizes of arr, 
    dp, current_arr 
    and maxSum */
    static int N = 105; 
    static int M = 1001; 
      
    // INF to define 
    // min value 
    static int INF = -1111111111; 
      
    // Function to find 
    // maximum sum 
    static int maxSum(int [][]arr) 
    { 
        // dp array of size N x M 
        int [][]dp = new int[N][M]; 
      
        // current_arr of size M 
        int []current_arr = new int[M]; 
      
        // maxsum of size M 
        int []maxsum = new int[M]; 
          
        for (int i = 0; i < N; i++) 
        { 
            for (int j = 0; j < M ; j++) 
                dp[i][j] = -1; 
        } 
      
        current_arr[0] = 0; 
      
        // if we have 0 elements 
        // from 0th array 
        dp[0][0] = 0; 
      
        for (int i = 1; i <= 5; i++) 
        { 
            int len = arr[i - 1][0]; 
      
            // compute the cumulative 
            // sum array 
            for (int j = 1; j <= len; j++) 
            { 
                current_arr[j] = arr[i - 1][j]; 
                current_arr[j] += current_arr[j - 1]; 
                maxsum[j] = INF; 
            } 
      
            // calculating the maximum 
            // contiguous array for every 
            // length j, j is from 1 to 
            // lengtn of the array 
            for (int j = 1; j <= len && j <= 6; j++) 
                for (int k = 1; k <= len; k++) 
                    if (j + k - 1 <= len) 
                        maxsum[j] = Math.max(maxsum[j], 
                                    current_arr[j + k - 1] - 
                                    current_arr[k - 1]); 
      
            // every state is depending 
            // on its previous state 
            for (int j = 0; j <= 6; j++) 
                dp[i][j] = dp[i - 1][j]; 
      
            // computation of dp table 
            // similar approach as 
            // knapsack problem 
            for (int j = 1; j <= 6; j++) 
                for (int cur = 1; cur <= j && 
                                cur <= len; cur++) 
                    dp[i][j] = Math.max(dp[i][j], 
                                        dp[i - 1][j - cur] + 
                                            maxsum[cur]); 
        } 
      
        // now we have done processing 
        // with the last array lets 
        // find out what is the maximum 
        // sum possible 
        int ans = 0; 
        for (int i = 0; i <= 6; i++) 
            ans = Math.max(ans, dp[5][i]); 
      
        return ans; 
    } 
      
    // Driver Code 
    public static void main(String args[]) 
    { 
        // first element of each 
        // row is the size of that row 
        int[][] arr = { 
                { 3, 2, 3, 5 }, 
                { 2, 7, -1 }, 
                { 2, 8, 10 }, 
                { 4, 5, 2, 6, 1 }, 
                { 3, 2, 3, -2 } 
        }; 
        System.out.println("Maximum sum can be " + 
                            "obtained is : " + 
                    maxSum(arr)); 
    } 
} 
  
// This code is contributed by 
// Manish Shaw(manishshaw1) 

Python3

# A Dynamic Programming based Python3 
# program to find maximum sum of array
# of size less than or equal to m from
# given n arrays
  
# N and M to define sizes of arr,
# dp, current_arr and maxSum 
N = 105
M = 1001
  
# INF to define min value
INF = -1111111111
  
# Function to find maximum sum
def maxSum(arr):
  
    # dp array of size N x M
    dp = [[-1 for x in range(M)]
              for y in range(N)]
  
    # current_arr of size M
    current_arr = [0] * M
  
    # maxsum of size M
    maxsum = [0] * M
  
    current_arr[0] = 0
  
    # If we have 0 elements
    # from 0th array
    dp[0][0] = 0
  
    for i in range(1, 6):
        len = arr[i - 1][0]
  
        # Compute the cumulative sum array
        for j in range(1, len + 1):
            current_arr[j] = arr[i - 1][j]
            current_arr[j] += current_arr[j - 1]
            maxsum[j] = INF
  
        # Calculating the maximum contiguous
        # array for every length j, j is from
        # 1 to lengtn of the array
        j = 1
        while j <= len and j <= 6:
            for k in range(1, len + 1):
                if (j + k - 1 <= len):
                    maxsum[j] = max(maxsum[j],
                               current_arr[j + k - 1] -
                               current_arr[k - 1])
                                 
            j += 1
  
        # Every state is depending on
        # its previous state
        for j in range(7):
            dp[i][j] = dp[i - 1][j]
  
        # computation of dp table similar
        # approach as knapsack problem
        for j in range(1, 7):
            cur = 1
            while cur <= j and cur <= len:
                dp[i][j] = max(dp[i][j],
                               dp[i - 1][j - cur] +
                                      maxsum[cur])
                                        
                cur += 1
  
    # Now we have done processing with
    # the last array lets find out
    # what is the maximum sum possible
    ans = 0
    for i in range(7):
        ans = max(ans, dp[5][i]) 
  
    return ans
  
# Driver code
if __name__ == "__main__":
  
    # First element of each
    # row is the size of that row
    arr = [ [ 3, 2, 3, 5 ],
            [ 2, 7, -1 ],
            [ 2, 8, 10 ],
            [ 4, 5, 2, 6, 1 ],
            [ 3, 2, 3, -2 ] ]
  
    print("Maximum sum can be obtained", 
          "is : ", maxSum(arr))
  
# This code is contributed by chitranayal

C#

// C# program to find maximum sum 
// of array of size less than or 
// equal to m from given n arrays 
using System; 
  
class GFG 
{ 
    /* N and M to define 
    sizes of arr, 
    dp, current_arr 
    and maxSum */
    static int N = 105; 
    static int M = 1001; 
      
    // INF to define 
    // min value 
    static int INF = -1111111111; 
      
    // Function to find 
    // maximum sum 
    static int maxSum(int [][]arr) 
    { 
        // dp array of size N x M 
        int [,]dp = new int[N, M]; 
      
        // current_arr of size M 
        int []current_arr = new int[M]; 
      
        // maxsum of size M 
        int []maxsum = new int[M]; 
          
        for (int i = 0; i < N; i++) 
        { 
            for (int j = 0; j < M ; j++) 
                dp[i, j] = -1; 
        } 
      
        current_arr[0] = 0; 
      
        // if we have 0 elements 
        // from 0th array 
        dp[0, 0] = 0; 
      
        for (int i = 1; i <= 5; i++) 
        { 
            int len = arr[i - 1][0]; 
      
            // compute the cumulative 
            // sum array 
            for (int j = 1; j <= len; j++) 
            { 
                current_arr[j] = arr[i - 1][j]; 
                current_arr[j] += current_arr[j - 1]; 
                maxsum[j] = INF; 
            } 
      
            // calculating the maximum 
            // contiguous array for every 
            // length j, j is from 1 to 
            // lengtn of the array 
            for (int j = 1; j <= len && j <= 6; j++) 
                for (int k = 1; k <= len; k++) 
                    if (j + k - 1 <= len) 
                        maxsum[j] = Math.Max(maxsum[j], 
                                    current_arr[j + k - 1] - 
                                    current_arr[k - 1]); 
      
            // every state is depending 
            // on its previous state 
            for (int j = 0; j <= 6; j++) 
                dp[i, j] = dp[i - 1, j]; 
      
            // computation of dp table 
            // similar approach as 
            // knapsack problem 
            for (int j = 1; j <= 6; j++) 
                for (int cur = 1; cur <= j && 
                                cur <= len; cur++) 
                    dp[i, j] = Math.Max(dp[i, j], 
                                        dp[i - 1, j - cur] + 
                                            maxsum[cur]); 
        } 
      
        // now we have done processing 
        // with the last array lets 
        // find out what is the maximum 
        // sum possible 
        int ans = 0; 
        for (int i = 0; i <= 6; i++) 
            ans = Math.Max(ans, dp[5, i]); 
      
        return ans; 
    } 
      
    // Driver Code 
    static void Main() 
    { 
        // first element of each 
        // row is the size of that row 
        int[][] arr = new int[][] 
        { 
            new int[]{ 3, 2, 3, 5 }, 
            new int[]{ 2, 7, -1 }, 
            new int[]{ 2, 8, 10 }, 
            new int[]{ 4, 5, 2, 6, 1 }, 
            new int[]{ 3, 2, 3, -2 } 
        }; 
        Console.Write ("Maximum sum can be " + 
                            "obtained is : " + 
                        maxSum(arr) + "\n"); 
    } 
} 
  
// This code is contributed by 
// Manish Shaw(manishshaw1) 