[Codility] Lesson4 - MissingInteger

Task discription

This is a demo task.
Write a function:
int solution(vector &A);
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].

Source Code

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int solution(vector<int> &A) {
    int ans = 1;
    
    // 정렬 & 중복제거
    sort(A.begin(), A.end());
    A.erase(unique(A.begin(), A.end()), A.end());
    
    for(int i=0;i<A.size();i++){
        if(ans == A[i])
            ans++;
        
    }
    return ans;
}