On a table are N cards, with a positive integer printed on the front and back of each card (possibly different).

We flip any number of cards, and after we choose one card.

If the number X on the back of the chosen card is not on the front of any card, then this number X is good.

What is the smallest number that is good? If no number is good, output 0.

Here, fronts[i] and backs[i] represent the number on the front and back of card i.

A flip swaps the front and back numbers, so the value on the front is now on the back and vice versa.

Example:

Input: fronts = [1,2,4,4,7], backs = [1,3,4,1,3]
Output: 2
Explanation: If we flip the second card, the
 
 fronts are [1,3,4,4,7] and the backs are [1,2,4,1,3].
We choose the second card, which has number 2 on the back, and it isn't on the front of any card, so 2 is good.

Note:

1 <= fronts.length == backs.length <= 1000.
1 <= fronts[i] <= 2000.
1 <= backs[i] <= 2000.

class Solution {
    public
 
 int flipgame(int[] fronts, int[] backs) {
        Set<Integer> same = new HashSet();
        for (int i = 0; i < fronts.length; ++i)
            if (fronts[i] == backs[i])
                same.add(fronts[i]);

        int ans = 9999;
        for (int x: fronts)
            if (!same.contains(x))
                ans = Math.min(ans, x);

        for (int x: backs)
            if (!same.contains(x))
                ans = Math.min(ans, x);

        return ans % 9999;
    }
}