Codility:MissingInteger

Write a function:

int solution(int A[], int N);

that, given a non-empty zero-indexed array A of N integers, returns the minimal positive integer (greater than 0) that does not occur in A.
For example, given:
A[0] = 1 A[1] = 3 A[2] = 6 A[3] = 4 A[4] = 1 A[5] = 2
the function should return 5.
Assume that:

• N is an integer within the range [1..100,000];
• each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].

Complexity:

• expected worst-case time complexity is O(N);
• expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).

Elements of input arrays can be modified.


https://codility.com/demo/results/trainingPNNDDK-MCG/
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace MissingInteger
{
    class Program
    {
        static void Main(string[] args)
        {
        }
    }
    public class Solution
    {
        public int solution(int[] A)
        {
            // write your code in C# 6.0 with .NET 4.5 (Mono)
            HashSet<int> set = new HashSet<int>(A);
            for (int i = 1; i <= A.Length + 1; i++)
            {
                if (!set.Contains(i))
                { return i; }
            }
            return -1;
        }
    }
}











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