PrefixSet

Task description
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<N and such that every value that occurs in array A also occurs in sequence A[0], A[1], ..., A[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 solution(int[] A); }
that, given a zero-indexed non-empty array A consisting of N integers, returns the first covering prefix of A.
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.
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].
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.

Solution:
// you can also use imports, for example:
// import java.math.*;
import java.util.HashSet;
class Solution {
    public int solution(int[] A) {
        // write your code in Java SE 7
        int resultIndex=0;
HashSet<Integer> h=new HashSet<Integer>();
for(int i=0;i<A.length;i++){
if(!h.contains(A[i])){
    h.add(A[i]);
    resultIndex=i;
}
}
return resultIndex;
    
}

}