Codility prefix_set Solution 100%

A non-empty zero-indexed array A consisting of N integers is given. The first covering prefix of array A is the smallest integer P such that 0≤P

For example, the first covering prefix of the following 5−element array A:

A[0] = 2  A[1] = 2  A[2] = 1
A[3] = 0  A[4] = 1

is 3, because sequence [ A[0], A[1], A[2], A[3] ] equal to [2, 2, 1, 0], contains all values that occur in array A.

Write a function

           class Solution { public int ps(int[] A); }

that, given a zero-indexed non-empty array A consisting of N integers, returns the first covering prefix of A.

Assume that:

• N is an integer within the range [1..1,000,000];
• each element of array A is an integer within the range [0..N−1].

For example, given array A such that

A[0] = 2  A[1] = 2  A[2] = 1
A[3] = 0  A[4] = 1

the function should return 3, as explained above.

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).

Solution:

import java.util.HashSet;
import java.util.Set;

class Solution {
  public int ps ( int[] A ) {
    Set set = new HashSet();
        int index =-1;

        for(int i=0;i