find the standard deviation of all nodes in a linked list in swift

main.swift
class Node {
    var value: Double
    var next: Node?
    
    init(value: Double) {
        self.value = value
    }
}

func standardDeviation(_ head: Node?) -> Double {
    // Step 1: Calculate the mean
    var current = head
    var sum = 0.0
    var count = 0
    while current != nil {
        sum += current!.value
        count += 1
        current = current?.next
    }
    let mean = sum / Double(count)
    
    // Step 2: Calculate the sum of squared differences
    current = head
    var squaredDiffsSum = 0.0
    while current != nil {
        squaredDiffsSum += pow(current!.value - mean, 2)
        current = current?.next
    }
    
    // Step 3: Divide the sum by the total number of nodes
    let variance = squaredDiffsSum / Double(count)
    
    // Step 4: Take the square root of the variance to get the standard deviation
    return sqrt(variance)
}
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