Task description

• Notice: X, Y and D are integers within the range [1..1,000,000,000]

Solution

At first, I used a while loop to solve this problem, but it resulted in a timeout. Since the input can be as large as 1,000,000,000, we cannot use an O(N) algorithm here.

Instead, we need to find the rule and derive the equation to solve the problem efficiently.

import Foundation
import Glibc


public func solution(_ X : Int, _ Y : Int, _ D : Int) -> Int {
    let rst: Int = Int((Y - X) / D)
    if Int((Y - X) % D) == 0 {
        return rst
    } else {
        return rst + 1
    }
}