FrogRiverOne.java

class Solution {
    public int solution(int X, int[] A) {
        int second = -1;
        int count = 0;
        boolean[] counter = new boolean[X];
        for (int i = 0; i < A.length; i++) {
            int pos = A[i];
            if (pos <= A.length && !counter[pos-1]) {
                counter[pos-1] = true;
                count++;
            }
            if (count == X) {
                second = i;
                break;
            }
        }
        return second;
    }
}