Learning Algorithms with JS, Python and Java #11: Count the Vowels

This series of articles follows Stephen Grider's Udemy course in three different languages.

Today's question is a simple introduction to regular expressions.

--- Directions
Write a function that returns the number of vowels
used in a string. Vowels are the characters 'a', 'e'
'i', 'o', and 'u'.
--- Examples
vowels('Hi There!') --> 3
vowels('Why do you ask?') --> 4
vowels('Why?') --> 0

1: Iterative Solution

JavaScript:

function vowels(str) {
  let count = 0;
  let checker = ['a', 'e', 'i', 'o', 'u'];
  for (char of str.toLowerCase()) {
    if (checker.includes(char)) {
      count++;
    }
  }
  return count;
}

Python:

def vowels(string):
    count = 0
    checker = ['a', 'e', 'i', 'o', 'u']
    for char in string.lower():
        if char in checker:
            count += 1
    return count

Java:

import java.util.Arrays;
import java.util.List;

static int vowels(String str) {
    int count = 0;
    List<Character> checker = Arrays.asList('a', 'e', 'i', 'o', 'u');
    for (char chr : str.toLowerCase().toCharArray()) {
        if (checker.contains(chr)) {
            count++;
        }
    }
    return count;
}

2: Using Regular Expression

JavaScript:

function vowels(str) {
  const matches = str.match(/[aeiou]/gi); // an array or null
  return matches ? matches.length : 0;
}

Python:

import re

def vowels(string):
    matches = re.findall('[aeiou]', string, re.IGNORECASE)  # a list
    return len(matches)

Java:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

static int vowels(String str) {
    Pattern pattern = Pattern.compile("[aeiou]", Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(str);
    int count = 0;
    while (matcher.find()) {
        count++;
    }
    return count;
}

Java 9+:

import java.util.regex.Pattern;

static long vowels(String str) {
    return Pattern.compile("[aeiou]", Pattern.CASE_INSENSITIVE)
            .matcher(str)
            .results()
            .count();
}