Kotlin Program to Count Words in a String

You can count words in a string in Kotlin by splitting the string with split(" ") and then getting the size of the resulting list using words.size.

Examples

InputHello world

Output2

InputKotlin is fun to learn

Output5

Input

Output0

How to Think About It

To count words, think of words as parts separated by spaces. Splitting the string by spaces creates a list of words. Counting the number of items in this list gives the total words. We must also handle empty strings carefully so they don't count as one word.

Algorithm

1

Get the input string.

2

Trim the string to remove extra spaces at the start and end.

3

Check if the string is empty after trimming; if yes, return 0.

4

Split the string by spaces to get a list of words.

5

Count the number of words in the list.

6

Return the count.

Code

kotlin

fun countWords(text: String): Int {
    val trimmed = text.trim()
    if (trimmed.isEmpty()) return 0
    val words = trimmed.split(" ")
    return words.size
}

fun main() {
    val input = "Kotlin is fun to learn"
    println("Word count: ${countWords(input)}")
}

Output

Word count: 5

Dry Run

Let's trace the input "Kotlin is fun to learn" through the code

1

Trim input

Input: "Kotlin is fun to learn" -> Trimmed: "Kotlin is fun to learn"

2

Check if empty

Trimmed string is not empty, continue

3

Split string

Split by space -> ["Kotlin", "is", "fun", "to", "learn"]

4

Count words

List size is 5

5

Return count

Return 5

Step	Action	Value
1	Trim input	"Kotlin is fun to learn"
2	Check empty	Not empty
3	Split string	["Kotlin", "is", "fun", "to", "learn"]
4	Count words	5
5	Return count	5

Why This Works

Step 1: Trim the string

We use trim() to remove spaces at the start and end so they don't count as empty words.

Step 2: Check for empty string

If the trimmed string is empty, it means there are no words, so we return 0.

Step 3: Split by spaces

Splitting the string by space creates a list where each element is a word.

Step 4: Count words

The size of the list is the total number of words in the string.

Alternative Approaches

Using Regex to split by any whitespace

kotlin

fun countWordsRegex(text: String): Int {
    val trimmed = text.trim()
    if (trimmed.isEmpty()) return 0
    val words = trimmed.split(Regex("\\s+"))
    return words.size
}

fun main() {
    val input = "Kotlin   is fun\tto learn"
    println("Word count: ${countWordsRegex(input)}")
}

This method handles multiple spaces and tabs between words better than splitting by a single space.

Using filter and count

kotlin

fun countWordsFilter(text: String): Int {
    return text.split(" ").filter { it.isNotBlank() }.count()
}

fun main() {
    val input = "  Kotlin  is  fun  "
    println("Word count: ${countWordsFilter(input)}")
}

This method removes empty strings from the split list, counting only real words.

Complexity: O(n) time, O(n) space

Time Complexity

The program scans the entire string once to trim and split it, so time grows linearly with string length.

Space Complexity

Splitting creates a list of words, which requires extra space proportional to the number of words.

Which Approach is Fastest?

Splitting by a simple space is fast but less flexible; regex splitting handles complex whitespace but is slightly slower.

Approach	Time	Space	Best For
Split by space	O(n)	O(n)	Simple cases with single spaces
Split by regex whitespace	O(n)	O(n)	Strings with multiple or mixed whitespace
Filter after split	O(n)	O(n)	Ignoring empty words after splitting