freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/count-occurrences-of-a-substring.md

title	id	challengeType	forumTopicId
Count occurrences of a substring	596fda99c69f779975a1b67d	5	302237

Description

Create a function, or show a built-in function, to count the number of non-overlapping occurrences of a substring inside a string. The function should take two arguments:

• the first argument being the string to search, and
• the second a substring to be searched for.

It should return an integer count. The matching should yield the highest number of non-overlapping matches. In general, this essentially means matching from left-to-right or right-to-left.

Instructions

Tests

tests:
  - text: <code>countSubstring</code> should be a function.
    testString: assert(typeof countSubstring === 'function');
  - text: <code>countSubstring("the three truths", "th")</code> should return <code>3</code>.
    testString: assert.equal(countSubstring(testCases[0], searchString[0]), results[0]);
  - text: <code>countSubstring("ababababab", "abab")</code> should return <code>2</code>.
    testString: assert.equal(countSubstring(testCases[1], searchString[1]), results[1]);
  - text: <code>countSubstring("abaabba*bbaba*bbab", "a*b")</code> should return <code>2</code>.
    testString: assert.equal(countSubstring(testCases[2], searchString[2]), results[2]);

Challenge Seed

function countSubstring(str, subStr) {

  return true;
}

After Test

const testCases = ['the three truths', 'ababababab', 'abaabba*bbaba*bbab'];
const searchString = ['th', 'abab', 'a*b'];
const results = [3, 2, 2];

Solution

function countSubstring(str, subStr) {
  const escapedSubStr = subStr.replace(/[.+*?^$[\]{}()|/]/g, '\\$&');
  const matches = str.match(new RegExp(escapedSubStr, 'g'));
  return matches ? matches.length : 0;
}