Find the minimum value of X for an expression

Given an array arr[]. The task is t find the value of X such that the result of the expression (A[1] - X)^2 + (A[2] - X)^2 + (A[3] - X)^2 + ... (A[n-1] - X)^2 + (A[n] – X)^2 is minimum possible.
Examples :

Input : arr[] = {6, 9, 1, 6, 1, 3, 7}
Output : 5
Input : arr[] = {1, 2, 3, 4, 5}
Output : 3

Approach:
We can simplify the expression that we need to minimize. The expression can be written as

(A[1]^2 + A[2]^2 + A[3]^2 + … + A[n]^2) + nX^2 – 2X(A[1] + A[2] + A[3] + … + A[n])

On differentiating the above expression, we get

 2nX - 2(A[1] + A[2] + A[3] + … + A[n])

We can denote the term (A[1] + A[2] + A[3] + … + A[n] ) as S. We get

 2nX - 2S

Putting 2nX - 2S = 0, we get

 X = S/N

Below is the implementation of the above approach:

C++

// C++ implementation of above approach

#include <bits/stdc++.h>
using namespace std;

// Function to calculate value of X
int valueofX(int ar[], int n)
{
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum = sum + ar[i];
    }

    if (sum % n == 0) {
        return sum / n;
    }
    else {
        int A = sum / n, B = sum / n + 1;
        int ValueA = 0, ValueB = 0;

        // Check for both possibilities
        for (int i = 0; i < n; i++) {
            ValueA += (ar[i] - A) * (ar[i] - A);
            ValueB += (ar[i] - B) * (ar[i] - B);
        }

        if (ValueA < ValueB) {
            return A;
        }
        else {
            return B;
        }
    }
}

// Driver Code
int main()
{
    int n = 7;
    int arr[7] = { 6, 9, 1, 6, 1, 3, 7 };

    cout << valueofX(arr, n) << '\n';

    return 0;
}

Java

// Java implementation of above approach
class GFG 
{

// Function to calculate value of X
static int valueofX(int ar[], int n)
{
    int sum = 0;
    for (int i = 0; i < n; i++)
    {
        sum = sum + ar[i];
    }

    if (sum % n == 0)
    {
        return sum / n;
    }
    else 
    {
        int A = sum / n, B = sum / n + 1;
        int ValueA = 0, ValueB = 0;

        // Check for both possibilities
        for (int i = 0; i < n; i++) 
        {
            ValueA += (ar[i] - A) * (ar[i] - A);
            ValueB += (ar[i] - B) * (ar[i] - B);
        }

        if (ValueA < ValueB)
        {
            return A;
        }
        else 
        {
            return B;
        }
    }
}

// Driver Code
public static void main(String args[]) 
{
    int n = 7;
    int arr[] = { 6, 9, 1, 6, 1, 3, 7 };

    System.out.println(valueofX(arr, n));
}
}

// This code is contributed by PrinciRaj1992

Python3

# Python3 implementation of above approach

# Function to calculate value of X
def valueofX(ar, n):
    summ = sum(ar)

    if (summ % n == 0):
        return summ // n
    else:
        A = summ // n
        B = summ // n + 1
        ValueA = 0
        ValueB = 0

        # Check for both possibilities
        for i in range(n):
            ValueA += (ar[i] - A) * (ar[i] - A)
            ValueB += (ar[i] - B) * (ar[i] - B)

        if (ValueA < ValueB):
            return A
        else:
            return B

# Driver Code
n = 7
arr = [6, 9, 1, 6, 1, 3, 7]

print(valueofX(arr, n))

# This code is contributed by Mohit Kumar

// C# implementation of above approach
using System;
                    
class GFG 
{

// Function to calculate value of X
static int valueofX(int []ar, int n)
{
    int sum = 0;
    for (int i = 0; i < n; i++)
    {
        sum = sum + ar[i];
    }

    if (sum % n == 0)
    {
        return sum / n;
    }
    else
    {
        int A = sum / n, B = sum / n + 1;
        int ValueA = 0, ValueB = 0;

        // Check for both possibilities
        for (int i = 0; i < n; i++) 
        {
            ValueA += (ar[i] - A) * (ar[i] - A);
            ValueB += (ar[i] - B) * (ar[i] - B);
        }

        if (ValueA < ValueB)
        {
            return A;
        }
        else
        {
            return B;
        }
    }
}

// Driver Code
public static void Main(String []args) 
{
    int n = 7;
    int []arr = { 6, 9, 1, 6, 1, 3, 7 };

    Console.WriteLine(valueofX(arr, n));
}
}

// This code is contributed by 29AjayKumar

JavaScript

<script>
// JavaScript implementation of above approach 

// Function to calculate value of X 
function valueofX(ar, n) 
{ 
    let sum = 0; 
    for (let i = 0; i < n; i++) { 
        sum = sum + ar[i]; 
    } 

    if (sum % n == 0) { 
        return Math.floor(sum / n); 
    } 
    else { 
        let A = Math.floor(sum / n), B = Math.floor(sum / n + 1); 
        let ValueA = 0, ValueB = 0; 

        // Check for both possibilities 
        for (let i = 0; i < n; i++) { 
            ValueA += (ar[i] - A) * (ar[i] - A); 
            ValueB += (ar[i] - B) * (ar[i] - B); 
        } 

        if (ValueA < ValueB) { 
            return A; 
        } 
        else { 
            return B; 
        } 
    } 
} 

// Driver Code 
    let n = 7; 
    let arr = [ 6, 9, 1, 6, 1, 3, 7 ]; 

    document.write(valueofX(arr, n) + "<br>"); 

// This code is contributed by Surbhi Tyagi.
</script>

Output:

Time Complexity: O(n)

Auxiliary Space: O(1)

Find the minimum value of X for an expression

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