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Recursion for Coding Interviews in Python

Count All Occurrences of a Number

In this lesson, we will learn how to count all occurrences of a key in a given array.

We'll cover the following...

What does “Count all Occurrences of a Number” mean?

Our task is to find the number of times a key occurs in an array.

For example:

Number of occurrences of a key
Number of occurrences of a key

Implementation

Python 3.5
def count(array, key) :
  # Base Case
  if array == []: 
      return 0
  # Recursive case1
  if array[0] == key:
      return 1 + count(array[1:], key)
  # Recursive case2
  else:
      return 0 + count(array[1:], key)
# Driver Code
array = [1, 2, 1, 4, 5, 1]
key  = 1
print(count(array, key))

Explanation

We need to count the number of times key occurs in an array. We do this by checking the first element. If the first element is the specified key, we will add 1 ...