Quiz 3: Contains 7s

MyPlayground.swift

  
import UIKit
import PlaygroundSupport

/*
 Let g(N) be the count of numbers that contain a 7 when you write out all the numbers from 1 to N.
 g(7) = 1
 g(20) = 2
 g(70) = 8
 g(100) = 19
 What is g(1000)?
 Write a computer program to compute g(N)

 */

func g(_ n: Int) -> Int {
    var count = 0
    for i in (1...n) {
        let text = String(i)
        count += text.contains("7") ? 1 : 0
    }
    return count
}
assert(g(7) == 1, "g(7) should be 1")
assert(g(20) == 2, "g(20) should be 2")
assert(g(70) == 8, "g(70) should be 8")
assert(g(100) == 19, "g(100) should be 19")
print("\(g(1000))")

// Ans = 271