Which of the following implementations correctly uses a local function to achieve this?
hard📝 Application Q15 of 15
Kotlin - Functions
You want to write a Kotlin function processNumbers that takes a list of integers and returns the sum of their squares. You decide to use a local function square inside it. Which of the following implementations correctly uses a local function to achieve this?
Afun processNumbers(nums: List<Int>): Int {
fun square(x: Int) = x * x
var sum = 0
for (n in nums) {
sum += n
}
return sum
}
Bfun processNumbers(nums: List<Int>): Int {
var sum = 0
for (n in nums) {
fun square(x: Int) = x * x
sum += square
}
return sum
}
Cfun processNumbers(nums: List<Int>): Int {
fun square(x: Int) = x * x
return nums.map square(it).sum()
}
Dfun processNumbers(nums: List<Int>): Int {
fun square(x: Int) = x * x
return nums.sumOf { square(it) }
}
Step-by-Step Solution
Solution:
Step 1: Understand local function usage and Kotlin collection functions
Local function 'square' should be declared once inside 'processNumbers'. Using Kotlin's 'sumOf' is concise and correct.
Step 2: Analyze each option
fun processNumbers(nums: List): Int {
fun square(x: Int) = x * x
return nums.sumOf { square(it) }
} correctly declares the local function once and uses it with sumOf { square(it) }. fun processNumbers(nums: List): Int {
var sum = 0
for (n in nums) {
fun square(x: Int) = x * x
sum += square
}
return sum
} declares 'square' inside the loop but calls it without argument square(n), compile error. fun processNumbers(nums: List): Int {
fun square(x: Int) = x * x
return nums.map square(it).sum()
} has syntax error: nums.map square(it).sum() missing lambda braces {}. fun processNumbers(nums: List): Int {
fun square(x: Int) = x * x
var sum = 0
for (n in nums) {
sum += n
}
return sum
} defines 'square' but uses sum += n, computes sum of numbers not squares.
Final Answer:
fun processNumbers(nums: List): Int {
fun square(x: Int) = x * x
return nums.sumOf { square(it) }
} -> Option D
Quick Check:
Local function + sumOf = fun processNumbers(nums: List): Int {
fun square(x: Int) = x * x
return nums.sumOf { square(it) }
} [OK]
Quick Trick:Declare local function once; use sumOf for concise sum [OK]
Common Mistakes:
MISTAKES
Calling local function without required arguments
Syntax error: missing braces in lambda expression
Defining local function but forgetting to use it
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