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

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

• Will the list ever be empty?
  • No. You can assume it has at least 2 numbers.
• Will the list ever have an odd number of entries?
  • No.

Plan the solution with appropriate visualizations and pseudocode.

General Idea: In order to be able to make pairs, every element in the list most occur an even number of times. Use a frequency map to check for that!

1) Create an empty dict for the frequency map 2) For each num in the list: a) Add 1 to the current frequency map value (default to 0) 3) For each count in the frequency map values: a) If the count is odd, return False 4) All counts were even, so return True

• To get an element from a dict with a default fallback value, try looking up the get() function.

def divide_list(nums): # Frequency map to count occurrences of each number frequency_map = {} for num in nums: frequency_map[num] = frequency_map.get(num, 0) + 1 # Check if all counts are even for count in frequency_map.values(): if count % 2 != 0: return False # An odd count found, can't divide into pairs return True # All counts are even, can divide into pairs