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Given an array and three numbers, maximize (x * a[i]) + (y * a[j]) + (z * a[k])
  • Difficulty Level : Hard
  • Last Updated : 16 Aug, 2018
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Given an array of n integers, and three integers x, y and z. maximise the value of (x * a[i]) + (y * a[j]) + (z * a[k]) where i ≤ j ≤ k.

Examples :

Input : arr[] = {-1, -2, -3, -4, -5} 
         x = 1 
         y = 2 
         z = -3 
Output: 12
Explanation: The maximized values is 
(1 * -1) + (2 * -1) + ( -3 * -5) = 12 

Input: arr[] = {1, 2, 3, 4, 5} 
       x = 1 
       y = 2  
       z = 3 
Output: 30 
(1*5 + 2*5 + 3*5) = 30

A simple solution is to run three nested loops to iterate through all triplets. For every triplet, compute the required value and keep track of maximum and finally return the same.

An efficient solution is to preocompute values and store them using extra space. The first key observation is i ≤ j ≤ k, so x*a[i] will always be the left maximum, and z*a[k] will always be the right maximum. Create a left array where we store the left maximums for every element. Create a right array where we store the right maximums for every element. Then for every element, calculate the maximum value of the function possible. For any index ind, the maximum at that position will always be (left[ind] + j * a[ind] + right[ind]), find the maximum of this value for every element in the array and that will be your answer.



Below is the implementation of the above approach

C++




// CPP program to find the maximum value of
// x*arr[i] + y*arr[j] + z*arr[k]
#include <bits/stdc++.h>
using namespace std;
  
// function to maximize the condition
int maximizeExpr(int a[], int n, int x, int y, 
                                        int z)
{
    // Traverse the whole array and compute
    // left maximum for every index. 
    int L[n];
    L[0] = x * a[0];
    for (int i = 1; i < n; i++) 
        L[i] = max(L[i - 1], x * a[i]);
  
    // Compute right maximum for every index. 
    int R[n];
    R[n-1] = z * a[n-1];
    for (int i = n - 2; i >= 0; i--)
        R[i] = max(R[i + 1], z * a[i]);
  
    // Traverse through the whole array to 
    // maximize the required expression.
    int ans = INT_MIN; 
    for (int i = 0; i < n; i++) 
          ans = max(ans, L[i] + y * a[i] + R[i]); 
  
    return ans;
}
      
// driver program to test the above funcion 
int main() 
{
   int a[] = {-1, -2, -3, -4, -5};
   int n = sizeof(a)/sizeof(a[0]);
   int x = 1, y = 2 , z = -3;
   cout << maximizeExpr(a, n, x, y, z) << endl;
   return 0;
}

Java




// Java program to find the maximum value 
// of x*arr[i] + y*arr[j] + z*arr[k]
import java.io.*;
  
class GFG {
  
    // function to maximize the condition
    static int maximizeExpr(int a[], int n, int x, 
                             int y, int z)
    {
        // Traverse the whole array and compute
        // left maximum for every index. 
        int L[] = new int[n];
        L[0] = x * a[0];
        for (int i = 1; i < n; i++) 
            L[i] = Math.max(L[i - 1], x * a[i]);
  
        // Compute right maximum for every index. 
        int R[] = new int[n];
        R[n - 1] = z * a[n - 1];
        for (int i = n - 2; i >= 0; i--)
            R[i] = Math.max(R[i + 1], z * a[i]);
  
        // Traverse through the whole array to 
        // maximize the required expression.
        int ans = Integer.MIN_VALUE; 
        for (int i = 0; i < n; i++) 
            ans = Math.max(ans, L[i] + y * a[i] +
                                         R[i]); 
  
        return ans;
    }
      
    // driver program to test the above funcion 
    public static void main(String[] args) 
    {
    int a[] = {-1, -2, -3, -4, -5};
    int n = a.length;
    int x = 1, y = 2 , z = -3;
    System.out.println(maximizeExpr(a, n, x, y, z));
    }
}
// This code is contributed by Prerna Saini

Python3




# Python3 program to find 
# the maximum value of
# x*arr[i] + y*arr[j] + z*arr[k]
import sys
  
# function to maximize
# the condition
def maximizeExpr(a, n, x, y, z):
  
    # Traverse the whole array 
    # and compute left maximum 
    # for every index. 
    L = [0] * n
    L[0] = x * a[0]
    for i in range(1, n):
        L[i] = max(L[i - 1], x * a[i])
  
    # Compute right maximum
    # for every index. 
    R = [0] * n
    R[n - 1] = z * a[n - 1]
    for i in range(n - 2, -1, -1):
        R[i] = max(R[i + 1], z * a[i])
  
    # Traverse through the whole 
    # array to maximize the
    # required expression.
    ans = -sys.maxsize 
    for i in range(0, n):
        ans = max(ans, L[i] + y * 
                       a[i] + R[i]) 
  
    return ans
  
# Driver Code
a = [-1, -2, -3, -4, -5]
n = len(a)
x = 1
y = 2
z = -3
print(maximizeExpr(a, n, x, y, z))
  
# This code is contributed
# by Smitha

C#




// C# program to find the maximum value 
// of x*arr[i] + y*arr[j] + z*arr[k]
using System;
  
class GFG {
  
    // function to maximize the condition
    static int maximizeExpr(int []a, int n,
                       int x, int y, int z)
    {
          
        // Traverse the whole array and
        // compute left maximum for every
        // index. 
        int []L = new int[n];
        L[0] = x * a[0];
        for (int i = 1; i < n; i++) 
            L[i] = Math.Max(L[i - 1], x * a[i]);
  
        // Compute right maximum for
        // every index. 
        int []R = new int[n];
        R[n - 1] = z * a[n - 1];
        for (int i = n - 2; i >= 0; i--)
            R[i] = Math.Max(R[i + 1], z * a[i]);
  
        // Traverse through the whole array to 
        // maximize the required expression.
        int ans = int.MinValue; 
        for (int i = 0; i < n; i++) 
            ans = Math.Max(ans, L[i] + 
                             y * a[i] + R[i]); 
  
        return ans;
    }
      
    // driver program to test the
    // above funcion 
    public static void Main() 
    {
        int []a = {-1, -2, -3, -4, -5};
        int n = a.Length;
        int x = 1, y = 2 , z = -3;
          
        Console.WriteLine(
              maximizeExpr(a, n, x, y, z));
    }
}
  
// This code is contributed by vt_m.

PHP




<?php
// PHP program to find the 
// maximum value of 
// x*arr[i]+ y*arr[j] + z*arr[k]
  
// function to maximize
// the condition
function maximizeExpr($a, $n
                      $x, $y, $z)
{
    // Traverse the whole array 
    // and compute left maximum 
    // for every index. 
    $L = array();
    $L[0] = $x * $a[0];
    for ($i = 1; $i < $n; $i++) 
        $L[$i] = max($L[$i - 1], 
                     $x * $a[$i]);
  
    // Compute right maximum
    // for every index. 
    $R = array();
    $R[$n - 1] = $z * $a[$n - 1];
    for ($i = $n - 2; $i >= 0; $i--)
        $R[$i] = max($R[$i + 1], 
                     $z * $a[$i]);
  
    // Traverse through the whole 
    // array to maximize the 
    // required expression.
    $ans = PHP_INT_MIN; 
    for ($i = 0; $i < $n; $i++) 
        $ans = max($ans, $L[$i] + 
                   $y * $a[$i] + $R[$i]); 
  
    return $ans;
}
      
// Driver Code
$a = array(-1, -2, -3, -4, -5);
$n = count($a);
$x = 1; $y = 2 ; $z = -3;
echo maximizeExpr($a, $n, $x, $y, $z);
  
// This code is contributed by anuj_67.
?>


Output :
12

Time complexity : O(n)
Auxiliary Space : O(n)

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