CODEWITHSUNDEEP
javascriptrecursion
Kabachok
Kabachok

Reputation: 603

Recursively count a number of vowels in a string (JavaScript)

Can anyone please tell me what I am doing wrong in my code? I need to count the number of vowel occurances in a string using recursion. The function isVowels checks if the character is a vowel and it works. But this code below doesn't work...

function countVowels(str) {
    var length = str.length;
    if (length == 0) {
        return 0;
    }
    if (isVowel(str.charAt(length)) == false) {
        return countVowels(str.substring(0, length - 1));
    }
    return 1 + countVowels(str.substring(0, length - 1));
}

Upvotes: 0

Views: 2071

Answers (1)

Bergi
Bergi

Reputation: 664195

Characters in a string are - just like elements in an array - zero-indexed. You will need to use .charAt(length-1), or you're getting the character after the end of the string (which yields the empty string). This should do it:

function countVowels(str) {
    var length = str.length;
    if (length == 0) {
        return 0;
    }
    if (isVowel(str.charAt(length - 1)) == false) {
        return countVowels(str.substring(0, length - 1));
    }
    return 1 + countVowels(str.substring(0, length - 1));
}

However, you could simplify this by not calling the recursive part twice, and counting from the front:

function countVowels(str) {
    if (str.length == 0)
        return 0;
    return (isVowel(str.charAt(0)) ? 1 : 0) + countVowels(str.slice(1));
}

Upvotes: 4

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