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Minimum number of operations on an array to make all elements 0
  • Last Updated : 11 May, 2021

Given an array arr[] of N integers and an integer cost, the task is to calculate the cost of making all the elements of the array 0 with the given operation. In a single operation, an index 0 ≤ i < N and an integer X > 0 can be chosen such that 0 ≤ i + X < N then elements can be updated as arr[i] = arr[i] – 1 and arr[i + X] = arr[i + X] + 1. If i + X ≥ N then only arr[i] will be updated but with twice the regular cost. Print the minimum cost required.
Examples: 
 

Input: arr[] = {1, 2, 4, 5}, cost = 1 
Output: 31 
Move 1: i = 0, X = 3, arr[] = {0, 2, 4, 6} (cost = 1) 
Moves 2 and 3: i = 1, X = 2, arr[] = {0, 0, 4, 8} (cost = 2) 
Moves 4, 5, 6 and 7: i = 2, X = 1, arr[] = {0, 0, 0, 12} (cost = 4) 
Move 8: i = 3, X > 0, arr[] = {0, 0, 0, 0} (cost = 24) 
Total cost = 1 + 2 + 4 + 24 = 31
Input: arr[] = {1, 1, 0, 5}, cost = 2 
Output: 32 
 

 

Approach: To minimize the cost, for every index i always choose X such that i + X = N – 1 i.e. the last element then minimum cost can be calculated as: 
 

  • Store the sum of the elements from arr[0] to arr[n – 2] in sum then update totalCost = cost * sum and arr[n – 1] = arr[n – 1] + sum.
  • Now the cost of making all the elements 0 except the last one has been calculated. And the cost of making the last element 0 can be calculated as totalCost = totalCost + (2 * cost * arr[n – 1]).

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 minimum cost
int minCost(int n, int arr[], int cost)
{
    int sum = 0, totalCost = 0;
 
    // Sum of all the array elements
    // except the last element
    for (int i = 0; i < n - 1; i++)
        sum += arr[i];
 
    // Cost of making all the array elements 0
    // except the last element
    totalCost += cost * sum;
 
    // Update the last element
    arr[n - 1] += sum;
 
    // Cost of making the last element 0
    totalCost += (2 * cost * arr[n - 1]);
 
    return totalCost;
}
 
// Driver code
int main()
{
    int arr[] = { 1, 2, 4, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int cost = 1;
    cout << minCost(n, arr, cost);
}

Java




// Java implementation of the approach
public class GfG
{
 
    // Function to return the minimum cost
    static int minCost(int n, int arr[], int cost)
    {
        int sum = 0, totalCost = 0;
     
        // Sum of all the array elements
        // except the last element
        for (int i = 0; i < n - 1; i++)
            sum += arr[i];
     
        // Cost of making all the array elements 0
        // except the last element
        totalCost += cost * sum;
     
        // Update the last element
        arr[n - 1] += sum;
     
        // Cost of making the last element 0
        totalCost += (2 * cost * arr[n - 1]);
     
        return totalCost;
    }
 
    // Driver code
    public static void main(String []args)
    {
         
        int arr[] = { 1, 2, 4, 5 };
        int n = arr.length;
        int cost = 1;
        System.out.println(minCost(n, arr, cost));
    }
}
 
// This code is contributed by Rituraj Jain

Python3




# Python3 implementation of the approach
 
# Function to return the minimum cost
def minCost(n, arr, cost):
 
    Sum, totalCost = 0, 0
 
    # Sum of all the array elements
    # except the last element
    for i in range(0, n - 1):
        Sum += arr[i]
 
    # Cost of making all the array elements 0
    # except the last element
    totalCost += cost * Sum
 
    # Update the last element
    arr[n - 1] += Sum
 
    # Cost of making the last element 0
    totalCost += (2 * cost * arr[n - 1])
 
    return totalCost
 
# Driver code
if __name__ == "__main__":
 
    arr = [1, 2, 4, 5]
    n = len(arr)
    cost = 1
    print(minCost(n, arr, cost))
 
# This code is contributed by Rituraj Jain

C#




// C# implementation of the approach
using System ;
 
class GfG
{
 
    // Function to return the minimum cost
    static int minCost(int n, int []arr, int cost)
    {
        int sum = 0, totalCost = 0;
     
        // Sum of all the array elements
        // except the last element
        for (int i = 0; i < n - 1; i++)
            sum += arr[i];
     
        // Cost of making all the array elements 0
        // except the last element
        totalCost += cost * sum;
     
        // Update the last element
        arr[n - 1] += sum;
     
        // Cost of making the last element 0
        totalCost += (2 * cost * arr[n - 1]);
     
        return totalCost;
    }
 
    // Driver code
    public static void Main()
    {
         
        int []arr = { 1, 2, 4, 5 };
        int n = arr.Length;
        int cost = 1;
        Console.WriteLine(minCost(n, arr, cost));
    }
}
 
// This code is contributed by Ryuga

PHP




<?php
// PHP implementation of the approach
 
// Function to return the minimum cost
function minCost($n, $arr, $cost)
{
    $sum = 0;
    $totalCost = 0;
 
    // Sum of all the array elements
    // except the last element
    for ($i = 0; $i < ($n - 1); $i++)
        $sum += $arr[$i];
 
    // Cost of making all the array
    // elements 0 except the last element
    $totalCost += $cost * $sum;
 
    // Update the last element
    $arr[$n - 1] += $sum;
 
    // Cost of making the last element 0
    $totalCost += (2 * $cost * $arr[$n - 1]);
 
    return $totalCost;
}
 
// Driver code
$arr = array( 1, 2, 4, 5 );
$n = sizeof($arr);
$cost = 1;
echo minCost($n, $arr, $cost);
 
// This code is contributed by ajit
?>

Javascript




<script>
    // Javascript implementation of the approach
     
    // Function to return the minimum cost
    function minCost(n, arr, cost)
    {
        let sum = 0, totalCost = 0;
       
        // Sum of all the array elements
        // except the last element
        for (let i = 0; i < n - 1; i++)
            sum += arr[i];
       
        // Cost of making all the array elements 0
        // except the last element
        totalCost += cost * sum;
       
        // Update the last element
        arr[n - 1] += sum;
       
        // Cost of making the last element 0
        totalCost += (2 * cost * arr[n - 1]);
       
        return totalCost;
    }
     
    let arr = [ 1, 2, 4, 5 ];
    let n = arr.length;
    let cost = 1;
    document.write(minCost(n, arr, cost));
     
</script>
Output: 
31

 

Time Complexity: O(n)
 

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