Introduction to Sets

A set is an unordered collection of elements without duplicate entries.
When printed, iterated or converted into a sequence, its elements will appear in an arbitrary order.

Example

>>> print set()
set([])

>>> print set('HackerRank')
set(['a', 'c', 'e', 'H', 'k', 'n', 'r', 'R'])

>>> print set([1,2,1,2,3,4,5,6,0,9,12,22,3])
set([0, 1, 2, 3, 4, 5, 6, 9, 12, 22])

>>> print set((1,2,3,4,5,5))
set([1, 2, 3, 4, 5])

>>> print set(set(['H','a','c','k','e','r','r','a','n','k']))
set(['a', 'c', 'r', 'e', 'H', 'k', 'n'])

>>> print set({'Hacker' : 'DOSHI', 'Rank' : 616 })
set(['Hacker', 'Rank'])

>>> print set(enumerate(['H','a','c','k','e','r','r','a','n','k']))
set([(6, 'r'), (7, 'a'), (3, 'k'), (4, 'e'), (5, 'r'), (9, 'k'), (2, 'c'), (0, 'H'), (1, 'a'), (8, 'n')])

Basically, sets are used for membership testing and eliminating duplicate entries.

Task

Now, let’s use our knowledge of sets and help Mickey.

Ms. Gabriel Williams is a botany professor at District College. One day, she asked her student Mickey to compute the average of all the plants with distinct heights in her greenhouse.

Formula used:

Average = (Sum of Distinct Heights)/(Total Number of Distinct Heights)

Function Description

Complete the average function in the editor below.

average has the following parameters:

• int arr: an array of integers

Returns

• float: the resulting float value rounded to 3 places after the decimal

Input Format

The first line contains the integer, N, the size of arr.
The second line contains the  space-separated integers, arr[i].

Constraints

0 < N ≤ 100

Sample Input

STDIN                                       Function
-----                                       --------
10                                          arr[] size N = 10
161 182 161 154 176 170 167 171 170 174     arr = [161, 181, ..., 174]

Sample Output

169.375

Explanation

Here, set ([154, 161, 167, 170, 171, 174, 176, 182]) is the set containing the distinct heights. Using the sum() and len() functions, we can compute the average. Average = 1355/8 = 169.375

Solution Implementation

# ========================
#       Information
# ========================

# Direct Link: https://www.hackerrank.com/challenges/py-introduction-to-sets/problem
# Difficulty: Easy
# Max Score: 10
# Language: Python

# ========================
#         Solution
# ========================

def average(array):
    '''Calculates the average of the array'''
    s = set(arr)
    return float(sum(s)) / len(s)
if __name__ == '__main__':
    n = int(input())
    arr = list(map(int, input().split()))
    result = average(arr)
    print(result)