Count Substring Occurrences

Count Substring Occurrences


This function should take a main string and a substring as inputs and return the number of occurrences of the substring within the main string. It should not be case-sensitive and may overlap.


Input: Two strings (str).

Output: Integer (int).


assert count_occurrences("hello world hello", "hello") == 2
assert count_occurrences("Hello World hello", "hello") == 2
assert count_occurrences("hello", "world") == 0
assert count_occurrences("hello world hello world hello", "world") == 2

How it’s used:

  • in a word processing software to highlight or replace all occurrences of a particular word or phrase;
  • in website scraping to count the number of times a particular keyword appears;
  • in an analytics application to analyze the frequency of certain words or phrases in a body of text.


  • both inputs should be strings: mainStr ∈ string and subStr ∈ string;
  • the main string can have any length, including zero: 0 <= length(mainStr) <= N;
  • the substring should not be an empty string: length(subStr) > 0.

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