Frequency Count - codepath/compsci_guides GitHub Wiki

Unit 2 Session 2 (Click for link to problem statements)

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

• What type should my function output be?
  • Your function should return a dictionary.

P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Loop through each entry in the list, and increment the count for that element by 1.

1) Create an empty dict to store the frequency map
2) For each number in the list
  a) If the number is not in the frequency map, map to 1
  b) Otherwise, increment the count in the frequency map by 1
3) Return the frequency map

⚠️ Common Mistakes

• Make sure your input numbers are your dict's keys, and your dict's values are the count of how many time that number appeared.

I-mplement

def count_occurrences(nums):
    frequency_map = {}
    for num in nums:
        if num in frequency_map[num]:
            frequency_map[num] += 1
        else:
            frequency_map[num] = 1
    return frequency_map

Alternative Solution

def count_occurrences(nums):
    frequency_map = {}
    for num in nums:
        if num not in frequency_map[num]:
            frequency_map[num] = 0
        frequency_map[num] += 1
    return frequency_map