[codility] Counting Elements - MissingInteger

문제

This is a demo task.

Write a function:

public func solution(_ A : inout [Int]) -> Int

that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.

For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.

Given A = [1, 2, 3], the function should return 4.

Given A = [−1, −3], the function should return 1.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [1..100,000];
• each element of array A is an integer within the range [−1,000,000..1,000,000].Copyright 2009–2021 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

 

문제 해설

가장 작은 양의 정수를 리턴

A 배열이 주어지면 순열이 아닌 형태 [1,2,3,4,6] 5를 리턴

[1,2,3] 4를 리턴

[-1, -3] 1을 리턴

 

구현 해설

set을 이용해서 순차적으로 배열을 순회하면서 값이 없으면 가장 작은 정수로 판단

 

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    // write your code in Swift 4.2.1 (Linux)
    let sets = Set<Int>(A)
    for index in 1...Int.max {
        if !sets.contains(index) {
            return index
        }
    }
    return -1
}