Frequency of Numbers
Input: `arr` (list). Return: Dict mapping number (as string key) to frequency.
Example
Input: 1, 2, 2, 3
Output: {'1': 1, '2': 2, '3': 1}
Run your code to see output
Input: `arr` (list). Return: Dict mapping number (as string key) to frequency.
Input: 1, 2, 2, 3
Output: {'1': 1, '2': 2, '3': 1}
Run your code to see output