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Unique subsequences of length K with given sum
• Difficulty Level : Expert
• Last Updated : 29 May, 2021

Given an array arr[] of N integers and two numbers K and S, the task is to print all the subsequence of length K with the sum S.
Examples:

Input: N = 5, K = 3, S = 20, arr[] = {4, 6, 8, 2, 12}
Output:
{6, 2, 12}
Explanation:
Only one subsequence of size 3 with a sum 20 is possible i.e., {6, 2, 12} and sum is 6 + 2 + 12 = 20
Input: N = 10, K = 5, S = 25, arr[] = {2, 4, 6, 8, 10, 12, 1, 2, 5, 7}
Output:
{10, 1, 2, 5, 7}
{4, 8, 1, 5, 7}
{4, 8, 10, 1, 2}
{4, 6, 12, 1, 2}
{4, 6, 8, 2, 5}
{2, 10, 1, 5, 7}
{2, 8, 12, 1, 2}
{2, 6, 10, 2, 5}
{2, 6, 8, 2, 7}
{2, 4, 12, 2, 5}
{2, 4, 10, 2, 7}
{2, 4, 8, 10, 1}
{2, 4, 6, 12, 1}
{2, 4, 6, 8, 5}

Approach: The idea is to use Backtracking to print all the subsequence with given sum S. Below are the steps:

• Iterate for all the value of the array arr[] and do the following:
1. If we include the current element in the resultant subsequence then, decrement K and the above value of current element to the sum S.
2. Recursively iterate from next index of the element to the end of the array to find the resultant subsequence.
3. If K is 0 and S is 0 then we got our one of the resultant subsequence of length K and sum S, print this subsequence and backtrack for the next resulting subsequence.
4. If we doesn’t include the current element then, find the resultant subsequence by excluding the current element and repeating the above procedure for the rest of the element in the array.
• Resultant array in the steps 3 will give all the possible subsequence of length K with given sum S.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach``#include ``using` `namespace` `std;` `// Function to find all the subsequences``// of a given length and having sum S``void` `comb(``int``* arr, ``int` `len, ``int` `r,``          ``int` `ipos, ``int``* op, ``int` `opos,``          ``int` `sum)``{` `    ``// Termination condition``    ``if` `(opos == r) {` `        ``int` `sum2 = 0;``        ``for` `(``int` `i = 0; i < opos; i++) {` `            ``// Add value to sum``            ``sum2 = sum2 + op[i];``        ``}` `        ``// Check if the resultant sum``        ``// equals to target sum``        ``if` `(sum == sum2) {` `            ``// If true``            ``for` `(``int` `i = 0; i < opos; i++)` `                ``// Print resultant array``                ``cout << op[i] << ``", "``;` `            ``cout << endl;``        ``}` `        ``// End this recursion stack``        ``return``;``    ``}``    ``if` `(ipos < len) {` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + 1,``             ``op, opos, sum);` `        ``op[opos] = arr[ipos];` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + 1,``             ``op, opos + 1, sum);``    ``}``}` `// Driver Code``int` `main()``{``    ``// Given array``    ``int` `arr[] = { 4, 6, 8, 2, 12 };``    ``int` `K = 3;``    ``int` `S = 20;` `    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr);` `    ``// To store the subsequence``    ``int` `op[N] = { 0 };` `    ``// Function Call``    ``comb(arr, N, K, 0, op, 0, S);``    ``return` `0;``}`

## Java

 `// Java program for the above approach``import` `java.util.*;` `class` `GFG{` `// Function to find all the subsequences``// of a given length and having sum S``static` `void` `comb(``int` `[]arr, ``int` `len, ``int` `r,``                 ``int` `ipos, ``int``[] op, ``int` `opos,``                 ``int` `sum)``{` `    ``// Termination condition``    ``if` `(opos == r)``    ``{``        ``int` `sum2 = ``0``;``        ``for``(``int` `i = ``0``; i < opos; i++)``        ``{``            ` `           ``// Add value to sum``           ``sum2 = sum2 + op[i];``        ``}` `        ``// Check if the resultant sum``        ``// equals to target sum``        ``if` `(sum == sum2)``        ``{` `            ``// If true``            ``for``(``int` `i = ``0``; i < opos; i++)``               ` `               ``// Print resultant array``               ``System.out.print(op[i] + ``", "``);` `            ``System.out.println();``        ``}` `        ``// End this recursion stack``        ``return``;``    ``}``    ``if` `(ipos < len)``    ``{` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + ``1``,``             ``op, opos, sum);``             ` `        ``op[opos] = arr[ipos];` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + ``1``,``             ``op, opos + ``1``, sum);``    ``}``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ` `    ``// Given array``    ``int` `arr[] = { ``4``, ``6``, ``8``, ``2``, ``12` `};``    ``int` `K = ``3``;``    ``int` `S = ``20``;` `    ``int` `N = arr.length;` `    ``// To store the subsequence``    ``int` `op[] = ``new` `int``[N];` `    ``// Function Call``    ``comb(arr, N, K, ``0``, op, ``0``, S);``}``}` `// This code is contributed by amal kumar choubey`

## Python3

 `# Python3 program for the above approach` `# Function to find all the subsequences``# of a given length and having sum S``def` `comb(arr, ``Len``, r, ipos, op, opos, ``Sum``):` `    ``# Termination condition``    ``if` `(opos ``=``=` `r):` `        ``sum2 ``=` `0``        ``for` `i ``in` `range``(opos):` `            ``# Add value to sum``            ``sum2 ``=` `sum2 ``+` `op[i]` `        ``# Check if the resultant sum``        ``# equals to target sum``        ``if` `(``Sum` `=``=` `sum2):` `            ``# If true``            ``for` `i ``in` `range``(opos):` `                ``# Print resultant array``                ``print``(op[i], end ``=` `", "``)` `            ``print``()` `        ``# End this recursion stack``        ``return` `    ``if` `(ipos < ``Len``):` `        ``# Check all the combinations``        ``# using backtracking``        ``comb(arr, ``Len``, r, ipos ``+` `1``,``             ``op, opos, ``Sum``)` `        ``op[opos] ``=` `arr[ipos]` `        ``# Check all the combinations``        ``# using backtracking``        ``comb(arr, ``Len``, r, ipos ``+` `1``, op,``                          ``opos ``+` `1``, ``Sum``)` `# Driver code``if` `__name__ ``=``=` `'__main__'``:` `    ``# Given array``    ``arr ``=` `[ ``4``, ``6``, ``8``, ``2``, ``12` `]``    ``K ``=` `3``    ``S ``=` `20``    ``N ``=` `len``(arr)` `    ``# To store the subsequence``    ``op ``=` `[``0``] ``*` `N` `    ``# Function call``    ``comb(arr, N, K, ``0``, op, ``0``, S)` `# This code is contributed by himanshu77`

## C#

 `// C# program for the above approach``using` `System;` `class` `GFG{` `// Function to find all the subsequences``// of a given length and having sum S``static` `void` `comb(``int` `[]arr, ``int` `len, ``int` `r,``                 ``int` `ipos, ``int``[] op, ``int` `opos,``                 ``int` `sum)``{` `    ``// Termination condition``    ``if` `(opos == r)``    ``{``        ``int` `sum2 = 0;``        ``for``(``int` `i = 0; i < opos; i++)``        ``{``           ` `           ``// Add value to sum``           ``sum2 = sum2 + op[i];``        ``}` `        ``// Check if the resultant sum``        ``// equals to target sum``        ``if` `(sum == sum2)``        ``{` `            ``// If true``            ``for``(``int` `i = 0; i < opos; i++)``               ` `               ``// Print resultant array``               ``Console.Write(op[i] + ``", "``);``            ``Console.WriteLine();``        ``}` `        ``// End this recursion stack``        ``return``;``    ``}``    ``if` `(ipos < len)``    ``{` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + 1,``             ``op, opos, sum);``            ` `        ``op[opos] = arr[ipos];` `        ``// Check all the combinations``        ``// using backtracking``        ``comb(arr, len, r, ipos + 1,``             ``op, opos + 1, sum);``    ``}``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ` `    ``// Given array``    ``int` `[]arr = { 4, 6, 8, 2, 12 };``    ``int` `K = 3;``    ``int` `S = 20;` `    ``int` `N = arr.Length;` `    ``// To store the subsequence``    ``int` `[]op = ``new` `int``[N];` `    ``// Function call``    ``comb(arr, N, K, 0, op, 0, S);``}``}` `// This code is contributed by amal kumar choubey`

## Javascript

 ``

Output:

`6, 2, 12, `

Time Complexity: O(N*N!)

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