# Find the subsequence with given sum in a superincreasing sequence

• Difficulty Level : Medium
• Last Updated : 07 Mar, 2022

A sequence of positive real numbers S1, S2, S3, …, SN is called a superincreasing sequence if every element of the sequence is greater than the sum of all the previous elements in the sequence. For example, 1, 3, 6, 13, 27, 52 is such subsequence.
Now, given a superincreasing sequence S and the sum of a subsequence of this sequence, the task is to find the subsequence.
Examples:

Input: S[] = {17, 25, 46, 94, 201, 400}, sum = 272
Output: 25 46 201
25 + 46 + 201 = 272
Input: S[] = {1, 2, 4, 8, 16}, sum = 12
Output: 4 8

Approach: This problem can be solved using the greedy technique. Starting from the last element of the array till the first element, there are two cases:

1. sum < arr[i]: In this case, the current element cannot be a part of the required subsequence as after including it, the sum of the subsequence will exceed the given sum. So discard the current element.
2. sum â‰¥ arr[i]: In this case, the current element has to be included in the required subsequence. This is because if the current element is not included then the sum of the previous elements in the array will be smaller than the current element (as it is a superincreasing sequence) which will in turn be smaller than the required sum. So take the current element and update the sum as sum = sum – arr[i].

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach` `#include ` `using` `namespace` `std;`   `// Function to find the required subsequence` `void` `findSubSeq(``int` `arr[], ``int` `n, ``int` `sum)` `{`   `    ``for` `(``int` `i = n - 1; i >= 0; i--) {`   `        ``// Current element cannot be a part` `        ``// of the required subsequence` `        ``if` `(sum < arr[i])` `            ``arr[i] = -1;`   `        ``// Include current element in` `        ``// the required subsequence` `        ``// So update the sum` `        ``else` `            ``sum -= arr[i];` `    ``}`   `    ``// Print the elements of the` `    ``// required subsequence` `    ``for` `(``int` `i = 0; i < n; i++) {`   `        ``// If the current element was` `        ``// included in the subsequence` `        ``if` `(arr[i] != -1)` `            ``cout << arr[i] << ``" "``;` `    ``}` `}`   `// Driver code` `int` `main()` `{` `    ``int` `arr[] = { 17, 25, 46, 94, 201, 400 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``);` `    ``int` `sum = 272;`   `    ``findSubSeq(arr, n, sum);`   `    ``return` `0;` `}`

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{` `    `  `    ``// Function to find the required subsequence ` `    ``static` `void` `findSubSeq(``int` `arr[], ``int` `n, ``int` `sum) ` `    ``{ ` `        ``for` `(``int` `i = n - ``1``; i >= ``0``; i--)` `        ``{ ` `    `  `            ``// Current element cannot be a part ` `            ``// of the required subsequence ` `            ``if` `(sum < arr[i]) ` `                ``arr[i] = -``1``; ` `    `  `            ``// Include current element in ` `            ``// the required subsequence ` `            ``// So update the sum ` `            ``else` `                ``sum -= arr[i]; ` `        ``} ` `    `  `        ``// Print the elements of the ` `        ``// required subsequence ` `        ``for` `(``int` `i = ``0``; i < n; i++) ` `        ``{ ` `    `  `            ``// If the current element was ` `            ``// included in the subsequence ` `            ``if` `(arr[i] != -``1``) ` `                ``System.out.print(arr[i] + ``" "``); ` `        ``} ` `    ``} ` `    `  `    ``// Driver code ` `    ``public` `static` `void` `main (String[] args) ` `    ``{ ` `        ``int` `arr[] = { ``17``, ``25``, ``46``, ``94``, ``201``, ``400` `}; ` `        ``int` `n = arr.length; ` `        ``int` `sum = ``272``; ` `    `  `        ``findSubSeq(arr, n, sum); ` `    ``} ` `}`   `// This code is contributed by AnkitRai01`

## Python3

 `# Python3 implementation of the approach `   `# Function to find the required subsequence ` `def` `findSubSeq(arr, n, ``sum``) : `   `    ``for` `i ``in` `range``(n ``-` `1``, ``-``1``, ``-``1``) :`   `        ``# Current element cannot be a part ` `        ``# of the required subsequence ` `        ``if` `(``sum` `< arr[i]) :` `            ``arr[i] ``=` `-``1``; `   `        ``# Include current element in ` `        ``# the required subsequence ` `        ``# So update the sum ` `        ``else` `:` `            ``sum` `-``=` `arr[i]; `   `    ``# Print the elements of the ` `    ``# required subsequence ` `    ``for` `i ``in` `range``(n) :`   `        ``# If the current element was ` `        ``# included in the subsequence ` `        ``if` `(arr[i] !``=` `-``1``) :` `            ``print``(arr[i], end ``=` `" "``); `   `# Driver code ` `if` `__name__ ``=``=` `"__main__"` `: `   `    ``arr ``=` `[ ``17``, ``25``, ``46``, ``94``, ``201``, ``400` `]; ` `    ``n ``=` `len``(arr); ` `    ``sum` `=` `272``; `   `    ``findSubSeq(arr, n, ``sum``); `   `# This code is contributed by kanugargng`

## C#

 `// C# implementation of the approach` `using` `System;` `    `  `class` `GFG ` `{` `    `  `    ``// Function to find the required subsequence ` `    ``static` `void` `findSubSeq(``int` `[]arr, ` `                           ``int` `n, ``int` `sum) ` `    ``{ ` `        ``for` `(``int` `i = n - 1; i >= 0; i--)` `        ``{ ` `    `  `            ``// Current element cannot be a part ` `            ``// of the required subsequence ` `            ``if` `(sum < arr[i]) ` `                ``arr[i] = -1; ` `    `  `            ``// Include current element in ` `            ``// the required subsequence ` `            ``// So update the sum ` `            ``else` `                ``sum -= arr[i]; ` `        ``} ` `    `  `        ``// Print the elements of the ` `        ``// required subsequence ` `        ``for` `(``int` `i = 0; i < n; i++) ` `        ``{ ` `    `  `            ``// If the current element was ` `            ``// included in the subsequence ` `            ``if` `(arr[i] != -1) ` `                ``Console.Write(arr[i] + ``" "``); ` `        ``} ` `    ``} ` `    `  `    ``// Driver code ` `    ``public` `static` `void` `Main (String[] args) ` `    ``{ ` `        ``int` `[]arr = { 17, 25, 46, 94, 201, 400 }; ` `        ``int` `n = arr.Length; ` `        ``int` `sum = 272; ` `    `  `        ``findSubSeq(arr, n, sum); ` `    ``} ` `}`   `// This code is contributed by PrinciRaj1992`

## Javascript

 ``

Output:

`25 46 201`

Time Complexity: O(n)

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