# Longest subsequence whose average is less than K

• Difficulty Level : Hard
• Last Updated : 30 Aug, 2022

Given an array of N positive integers and Q queries consisting of an integer K, the task is to print the length of the longest subsequence whose average is less than K.

Examples:

Input: a[] = {1, 3, 2, 5, 4}
Query1: K = 3
Query2: K = 5

Output:

Query1: The subsequence is: {1, 3, 2, 4} or {1, 3, 2, 5}
Query2: The subsequence is: {1, 3, 2, 5, 4}

A Naive Approach is to generate all subsequences using power-set and check for the longest subsequence whose average is less than K.
Time Complexity: O(2N * N )

An efficient approach is to sort the array elements and find the average of elements starting from the left. Insert the average of elements computed from the left into the container(vector or arrays). Sort the container’s element and then use binary search to search for the number K in the container. The length of the longest subsequence will thus be the index number which upper_bound() returns for every query.

Below is the implementation of the above approach.

## C++

 `// C++ program to perform Q queries` `// to find longest subsequence whose` `// average is less than K` `#include ` `using` `namespace` `std;`   `// Function to print the length for every query` `int` `longestSubsequence(``int` `a[], ``int` `n, ``int` `q[], ``int` `m)` `{`   `    ``// sort array of N elements` `    ``sort(a, a + n);` `    ``int` `sum = 0;`   `    ``// Array to store average from left` `    ``int` `b[n];`   `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``sum += a[i];` `        ``double` `av = (``double``)(sum) / (``double``)(i + 1);` `        ``b[i] = ((``int``)(av + 1));` `    ``}`   `    ``// Sort array of average` `    ``sort(b, b + n);`   `    ``// number of queries`   `    ``for` `(``int` `i = 0; i < m; i++) {` `        ``int` `k = q[i];`   `        ``// print answer to every query` `        ``// using binary search` `        ``int` `longest = upper_bound(b, b + n, k) - b;`   `        ``cout << ``"Answer to Query"` `<< i + 1 << ``": "` `             ``<< longest << endl;` `    ``}` `}`   `// Driver Code` `int` `main()` `{` `    ``int` `a[] = { 1, 3, 2, 5, 4 };` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a[0]);`   `    ``// 4 queries` `    ``int` `q[] = { 4, 2, 1, 5 };` `    ``int` `m = ``sizeof``(q) / ``sizeof``(q[0]);`   `    ``longestSubsequence(a, n, q, m);` `    ``return` `0;` `}`

## Java

 `// Java program to perform Q queries` `// to find longest subsequence whose` `// average is less than K` `import` `java.util.Arrays;`   `class` `GFG ` `{`   `    ``// Function to print the length for every query` `    ``static` `void` `longestSubsequence(``int` `a[], ``int` `n, ` `                                    ``int` `q[], ``int` `m)` `    ``{`   `        ``// sort array of N elements` `        ``Arrays.sort(a);` `        ``int` `sum = ``0``;`   `        ``// Array to store average from left` `        ``int` `[]b = ``new` `int``[n];`   `        ``for` `(``int` `i = ``0``; i < n; i++)` `        ``{` `            ``sum += a[i];` `            ``double` `av = (``double``)(sum) / (``double``)(i + ``1``);` `            ``b[i] = ((``int``)(av + ``1``));` `        ``}`   `        ``// Sort array of average` `        ``Arrays.sort(b);`   `        ``// number of queries`   `        ``for` `(``int` `i = ``0``; i < m; i++) ` `        ``{` `            ``int` `k = q[i];`   `            ``// print answer to every query` `            ``// using binary search` `            ``int` `longest = upperBound(b,``0``, n, k);`   `            ``System.out.println(``"Answer to Query"` `+ (i + ``1``) +``": "` `                ``+ longest);` `        ``}` `    ``}` `    ``private` `static` `int` `upperBound(``int``[] a, ``int` `low, ``int` `high, ``int` `element)` `    ``{` `        ``while``(low < high)` `        ``{` `            ``int` `middle = low + (high - low)/``2``;` `            ``if``(a[middle] > element)` `                ``high = middle;` `            ``else` `                ``low = middle + ``1``;` `        ``}` `        ``return` `low;` `    ``}` `    `  `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args) ` `    ``{` `        ``int` `a[] = { ``1``, ``3``, ``2``, ``5``, ``4` `};` `        ``int` `n = a.length;`   `        ``// 4 queries` `        ``int` `q[] = { ``4``, ``2``, ``1``, ``5` `};` `        ``int` `m = q.length;`   `        ``longestSubsequence(a, n, q, m); ` `    ``}` `}`   `/* This code contributed by PrinciRaj1992 */`

## Python3

 `# Python3 program to perform Q queries to find ` `# longest subsequence whose average is less than K ` `import` `bisect`   `# Function to print the length for every query ` `def` `longestSubsequence(a, n, q, m): ` ` `  `    ``# sort array of N elements ` `    ``a.sort() ` `    ``Sum` `=` `0`   `    ``# Array to store average from left ` `    ``b ``=` `[``None``] ``*` `n `   `    ``for` `i ``in` `range``(``0``, n):  ` `        ``Sum` `+``=` `a[i] ` `        ``av ``=` `Sum` `/``/` `(i ``+` `1``) ` `        ``b[i] ``=` `av ``+` `1`   `    ``# Sort array of average ` `    ``b.sort() `   `    ``# number of queries `   `    ``for` `i ``in` `range``(``0``, m):  ` `        ``k ``=` `q[i] `   `        ``# print answer to every query ` `        ``# using binary search ` `        ``longest ``=` `bisect.bisect_right(b, k) `   `        ``print``(``"Answer to Query"``, i ``+` `1``, ``":"``, longest)`   `# Driver Code ` `if` `__name__ ``=``=` `"__main__"``:` ` `  `    ``a ``=` `[``1``, ``3``, ``2``, ``5``, ``4``]  ` `    ``n ``=` `len``(a) `   `    ``# 4 queries ` `    ``q ``=` `[``4``, ``2``, ``1``, ``5``]  ` `    ``m ``=` `len``(q)`   `    ``longestSubsequence(a, n, q, m) ` `    `  `# This code is contributed by Rituraj Jain`

## C#

 `// C# program to perform Q queries` `// to find longest subsequence whose` `// average is less than K` `using` `System;`   `class` `GFG` `{` `    `  `    ``// Function to print the length for every query` `    ``static` `void` `longestSubsequence(``int` `[]a, ``int` `n, ` `                                    ``int` `[]q, ``int` `m)` `    ``{`   `        ``// sort array of N elements` `        ``Array.Sort(a);` `        ``int` `sum = 0;`   `        ``// Array to store average from left` `        ``int` `[]b = ``new` `int``[n];`   `        ``for` `(``int` `i = 0; i < n; i++)` `        ``{` `            ``sum += a[i];` `            ``double` `av = (``double``)(sum) / (``double``)(i + 1);` `            ``b[i] = ((``int``)(av + 1));` `        ``}`   `        ``// Sort array of average` `        ``Array.Sort(b);`   `        ``// number of queries`   `        ``for` `(``int` `i = 0; i < m; i++) ` `        ``{` `            ``int` `k = q[i];`   `            ``// print answer to every query` `            ``// using binary search` `            ``int` `longest = upperBound(b,0, n, k);`   `            ``Console.WriteLine(``"Answer to Query"` `+ (i + 1) +``": "` `                ``+ longest);` `        ``}` `    ``}` `    `  `    ``private` `static` `int` `upperBound(``int``[] a, ``int` `low, ` `                                    ``int` `high, ``int` `element)` `    ``{` `        ``while``(low < high)` `        ``{` `            ``int` `middle = low + (high - low)/2;` `            ``if``(a[middle] > element)` `                ``high = middle;` `            ``else` `                ``low = middle + 1;` `        ``}` `        ``return` `low;` `    ``}` `    `  `    ``// Driver Code` `    ``static` `public` `void` `Main ()` `    ``{` `        ``int` `[]a = { 1, 3, 2, 5, 4 };` `        ``int` `n = a.Length;`   `        ``// 4 queries` `        ``int` `[]q = { 4, 2, 1, 5 };` `        ``int` `m = q.Length;`   `        ``longestSubsequence(a, n, q, m); ` `    ``}` `}` `    `  `/* This code contributed by ajit */`

## Javascript

 ``

Output

```Answer to Query1: 5