2021-09-28

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


public class offerTest03 {
    public static void main(String[] args) {
        int[] ints = {1, 3, 4, 5, 1, 2, 3, 6};
        System.out.println(offerTest03.findRepeatNumber(ints));
    }


    public static int findRepeatNumber(int[] nums) {
        Set set = new HashSet();

        for (int num : nums) {
            if (!set.add(num)) {
                return num;
            }
        }
        return -1;
    }



   
}