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Sum of minimum element of all sub-sequences of a sorted array
  • Difficulty Level : Medium
  • Last Updated : 29 Apr, 2021

Given a sorted array A of n integers. The task is to find the sum of the minimum of all possible subsequences of A.
Note: Considering there will be no overflow of numbers.

Examples: 

Input: A = [1, 2, 4, 5] 
Output: 29 
Subsequences are [1], [2], [4], [5], [1, 2], [1, 4], [1, 5], [2, 4], [2, 5], [4, 5] [1, 2, 4], [1, 2, 5], [1, 4, 5], [2, 4, 5], [1, 2, 4, 5] 
Minimums are 1, 2, 4, 5, 1, 1, 1, 2, 2, 4, 1, 1, 1, 2, 1. 
Sum is 29
Input: A = [1, 2, 3] 
Output: 11  

Approach: The Naive approach is to generate all possible subsequences, find their minimum and add them to the result. 
Efficient Approach: It is given that the array is sorted, so observe that the minimum element occurs 2n-1 times, the second minimum occurs 2n-2 times, and so on… Let’s take an example: 

arr[] = {1, 2, 3} 
Subsequences are {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3} 
Minimum of each subsequence: {1}, {2}, {3}, {1}, {1}, {2}, {1}. 
where 
1 occurs 4 times i.e. 2 n-1 where n = 3. 
2 occurs 2 times i.e. 2n-2 where n = 3. 
3 occurs 1 times i.e. 2n-3 where n = 3.



So, traverse the array and add current element i.e. arr[i]* pow(2, n-1-i) to the sum.
Below is the implementation of the above approach: 
 

C++




// C++ implementation of the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the sum
// of minimum of all subsequence
int findMinSum(int arr[], int n)
{
 
    int occ = n - 1, sum = 0;
    for (int i = 0; i < n; i++) {
        sum += arr[i] * pow(2, occ);
        occ--;
    }
 
    return sum;
}
 
// Driver code
int main()
{
    int arr[] = { 1, 2, 4, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
 
    cout << findMinSum(arr, n);
 
    return 0;
}

Java




// Java implementation of the above approach
class GfG
{
 
// Function to find the sum
// of minimum of all subsequence
static int findMinSum(int arr[], int n)
{
 
    int occ = n - 1, sum = 0;
    for (int i = 0; i < n; i++)
    {
        sum += arr[i] * (int)Math.pow(2, occ);
        occ--;
    }
 
    return sum;
}
 
// Driver code
public static void main(String[] args)
{
    int arr[] = { 1, 2, 4, 5 };
    int n = arr.length;
 
    System.out.println(findMinSum(arr, n));
}
}
 
// This code is contributed by Prerna Saini

Python3




# Python3 implementation of the
# above approach
 
# Function to find the sum
# of minimum of all subsequence
def findMinSum(arr, n):
 
    occ = n - 1
    Sum = 0
    for i in range(n):
        Sum += arr[i] * pow(2, occ)
        occ -= 1
     
    return Sum
 
# Driver code
arr = [1, 2, 4, 5]
n = len(arr)
 
print(findMinSum(arr, n))
 
# This code is contributed
# by mohit kumar

C#




// C# implementation of the above approach
using System;
 
class GFG
{
     
// Function to find the sum
// of minimum of all subsequence
static int findMinSum(int []arr, int n)
{
 
    int occ = n - 1, sum = 0;
    for (int i = 0; i < n; i++)
    {
        sum += arr[i] *(int) Math.Pow(2, occ);
        occ--;
    }
 
    return sum;
}
 
// Driver code
public static void Main(String []args)
{
    int []arr = { 1, 2, 4, 5 };
    int n = arr.Length;
 
    Console.WriteLine( findMinSum(arr, n));
}
}
// This code is contributed by Arnab Kundu

PHP




<?php
// PHP implementation of the
// above approach
 
// Function to find the sum
// of minimum of all subsequence
function findMinSum($arr, $n)
{
    $occ1 = ($n);
    $occ = $occ1 - 1;
    $Sum = 0;
    for ($i = 0; $i < $n; $i++)
    {
        $Sum += $arr[$i] * pow(2, $occ);
        $occ -= 1;
    }
    return $Sum;
}
 
// Driver code
$arr = array(1, 2, 4, 5);
$n = count($arr);
 
echo findMinSum($arr, $n);
 
// This code is contributed
// by Srathore
?>

Javascript




<script>
 
// Javascript implementation of the above approach
 
// Function to find the sum
// of minimum of all subsequence
function findMinSum(arr, n)
{
 
    var occ = n - 1, sum = 0;
    for (var i = 0; i < n; i++) {
        sum += arr[i] * Math.pow(2, occ);
        occ--;
    }
 
    return sum;
}
 
// Driver code
var arr = [ 1, 2, 4, 5 ];
var n = arr.length;
document.write( findMinSum(arr, n));
 
</script>
Output: 
29

 

Note: To find the Sum of maximum element of all subsequences in a sorted array, just traverse the array in reverse order and apply the same formula for Sum.
 

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