Approaches for finding the most common integer in an array.

common1.py

# Constraints: an array of size n of integers in the range 0 to k-1, where k is a positive integer and k <= n
test = [0, 1, 1, 1, 3, 17, 5, 3, 2, 1, 9] # k = 10, n = 11
get_common(test, 10)

def get_common(A, k):
    """Return the most popular integer in an array. O(n) time, O(k) space."""

    # Create a lookup array with length k to track the occurrence of each possible member.
    # O(k) space
    lookup = [0] * k

    # For each element in A, increment the count in the lookup array at position `el`
    # O(n)
    for el in A:
        lookup[el] += 1

    # Iterate through the lookup array to find the max count
    max_count = 0 # O(1) space
    result = 0
    
    # O(k)
    for i range(0, k):
        if lookup[i] > max_count:
            max_count = lookup[i]
            result = i

    return result