Coding problem · Easy · Basics

Count the Vowels

Easy Algorithms & data structures

Return the number of vowels in s. Vowels are a, e, i, o and u, in upper or lower case.

Example 1

Input: s = "Hello World"
Output: 3

Example 2

Input: s = "sky"
Output: 0

Hints

Hint 1

Loop over the characters and check whether each one is in the set of vowels.

Hint 2

Lower-case the character (or the whole string) first so 'A' and 'a' both count.

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Solution and explanation

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Time O(n) · Space O(1)

Lower-case each character and count it if it's one of the five vowels. A set (or a string of vowels) makes the membership check simple.

Reference solution

function countVowels(s) {
  let count = 0;
  for (const ch of s.toLowerCase()) if ('aeiou'.includes(ch)) count++;
  return count;
}

function countVowels(s: string): number {
  let count = 0;
  for (const ch of s.toLowerCase()) if ('aeiou'.includes(ch)) count++;
  return count;
}

def count_vowels(s: str) -> int:
    return sum(1 for ch in s.lower() if ch in 'aeiou')

<?php

function countVowels(string $s): int
{
    return preg_match_all('/[aeiou]/i', $s);
}

class Solution {
    public int countVowels(String s) {
        int count = 0;
        for (char ch : s.toLowerCase().toCharArray()) if ("aeiou".indexOf(ch) >= 0) count++;
        return count;
    }
}

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