Given an array, task is to compute the sum of all possible maximum area rectangle which can be formed from the array elements. Also, you can reduce the elements of the array by at most 1.

**Examples :**

Input :a = {10, 10, 10, 10, 11, 10, 11, 10} Output : 210Explanation :We can form two rectangles one square (10 * 10) and one (11 * 10). Hence, total area = 100 + 110 = 210. Input : a = { 3, 4, 5, 6 } Output : 15 Explanation : We can reduce 4 to 3 and 6 to 5 so that we got rectangle of (3 * 5). Hence area = 15. Input : a = { 3, 2, 5, 2 } Output : 0

**Naive Approach : **Check for all possible four elements of the array and then whichever can form a rectangle. In these rectangles, separate all those rectangles which are of maximum area formed by these elements. After getting the rectangles and their areas, sum them all to get our desired solution.

**Efficient Approach :** To get the maximum area rectangle, first sort the elements of the array in non-increasing array. After sorting, start the procedure to select the elements of the array. Here, selection of two elements of array (as length of rectangle) is possible if elements of array are equal *(a[i] == a[i+1])* or if length of smaller element a[i+1] is one less than a[i] (*in this case we have our length a[i+1] because a[i] is decreased by 1*). One flag variable is maintained to check that *whether we get length and breadth both.* After getting length, set the flag variable, now calculate the breadth in the same way as we have done for length and sum the area of rectangle. After getting length and breadth both, again set the flag variable false so that we will now search for a new rectangle. This process is repeated and lastly, final sum of area is returned.

## C++

[sourcecode language=”CPP”]

// CPP code to find sum of all

// area rectangle possible

#include <bits/stdc++.h>

using namespace std;

// Function to find

// area of rectangles

int MaxTotalRectangleArea(int a[],

int n)

{

// sorting the array in

// descending order

sort(a, a + n, greater<int>());

// store the final sum of

// all the rectangles area

// possible

int sum = 0;

bool flag = false;

// temporary variable to store

// the length of rectangle

int len;

for (int i = 0; i < n; i++)

{

// Selecting the length of

// rectangle so that difference

// between any two number is 1

// only. Here length is selected

// so flag is set

if ((a[i] == a[i + 1] || a[i] –

a[i + 1] == 1) && (!flag))

{

// flag is set means

// we have got length of

// rectangle

flag = true;

// length is set to

// a[i+1] so that if

// a[i] a[i+1] is less

// than by 1 then also

// we have the correct

// choice for length

len = a[i + 1];

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

i++;

}

// Selecting the width of rectangle

// so that difference between any

// two number is 1 only. Here width

// is selected so now flag is again

// unset for next rectangle

else if ((a[i] == a[i + 1] ||

a[i] – a[i + 1] == 1) && (flag))

{

// area is calculated for

// rectangle

sum = sum + a[i + 1] * len;

// flag is set false

// for another rectangle

// which we can get from

// elements in array

flag = false;

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

i++;

}

}

return sum;

}

// Driver code

int main()

{

int a[] = { 10, 10, 10, 10,

11, 10, 11, 10,

9, 9, 8, 8 };

int n = sizeof(a) / sizeof(a[0]);

cout << MaxTotalRectangleArea(a, n);

return 0;

}

[/sourcecode]

## C#

[sourcecode language=”csharp”]

// C# code to find sum of all area rectangle

// possible

using System;

class GFG {

// Function to find

// area of rectangles

static int MaxTotalRectangleArea(int []a,

int n)

{

// sorting the array in descending

// order

Array.Sort(a);

// store the final sum of all the

// rectangles area possible

int sum = 0;

bool flag = false;

// temporary variable to store the

// length of rectangle

int len =0;

for (int i = 0; i < n; i++)

{

// Selecting the length of

// rectangle so that difference

// between any two number is 1

// only. Here length is selected

// so flag is set

if ((a[i] == a[i + 1] || a[i] –

a[i + 1] == 1) && (!flag))

{

// flag is set means

// we have got length of

// rectangle

flag = true;

// length is set to

// a[i+1] so that if

// a[i] a[i+1] is less

// than by 1 then also

// we have the correct

// choice for length

len = a[i + 1];

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

i++;

}

// Selecting the width of rectangle

// so that difference between any

// two number is 1 only. Here width

// is selected so now flag is again

// unset for next rectangle

else if ((a[i] == a[i + 1] ||

a[i] – a[i + 1] == 1) && (flag))

{

// area is calculated for

// rectangle

sum = sum + a[i + 1] * len;

// flag is set false

// for another rectangle

// which we can get from

// elements in array

flag = false;

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

i++;

}

}

return sum;

}

// Driver code

static public void Main ()

{

int []a = { 10, 10, 10, 10,

11, 10, 11, 10,

9, 9, 8, 8 };

int n = a.Length;

Console.WriteLine(

MaxTotalRectangleArea(a, n));

}

}

// This code is contributed by anuj_67.

[/sourcecode]

## PHP

[sourcecode language=”PHP”]

<?php

// PHP code to find sum

// of all area rectangle

// possible

// Function to find

// area of rectangles

function MaxTotalRectangleArea( $a, $n)

{

// sorting the array in

// descending order

rsort($a);

// store the final sum of

// all the rectangles area

// possible

$sum = 0;

$flag = false;

// temporary variable to store

// the length of rectangle

$len;

for ( $i = 0; $i < $n; $i++)

{

// Selecting the length of

// rectangle so that difference

// between any two number is 1

// only. Here length is selected

// so flag is set

if (($a[$i] == $a[$i + 1] or $a[$i] –

$a[$i + 1] == 1) and (!$flag))

{

// flag is set means

// we have got length of

// rectangle

$flag = true;

// length is set to

// a[i+1] so that if

// a[i+1] is less than a[i]

// by 1 then also we have

// the correct chice for length

$len = $a[$i + 1];

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

$i++;

}

// Selecting the width of rectangle

// so that difference between any

// two number is 1 only. Here width

// is selected so now flag is again

// unset for next rectangle

else if (($a[$i] == $a[$i + 1] or

$a[$i] – $a[$i + 1] == 1) and

($flag))

{

// area is calculated for

// rectangle

$sum = $sum + $a[$i + 1] * $len;

// flag is set false

// for another rectangle

// which we can get from

// elements in array

$flag = false;

// incrementing the counter

// one time more as we have

// considered a[i+1] element

// also so.

$i++;

}

}

return $sum;

}

// Driver code

$a = array( 10, 10, 10, 10,

11, 10, 11, 10,

9, 9, 8, 8 );

$n = count($a);

echo MaxTotalRectangleArea($a, $n);

//This code is contributed by anuj_67.

?>

[/sourcecode]

**Output :**

282

Time Complexity : **O(nlog(n))**

Auxiliary Space : **O(1)**

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