822_card_flipping_game.py

'''
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:
    def flipgame(self, fronts, backs):
        """
        :type fronts: List[int]
        :type backs: List[int]
        :rtype: int
        """
        min_value = 2001
        for i in range(len(fronts)):
            if fronts[i]==backs[i]: continue
            else:
                fronts[i], backs[i] = backs[i],fronts[i]
                if fronts.count(fronts[i]) == 1:
                    min_value = min(min_value, i+1)
            fronts[i], backs[i] = backs[i], fronts[i]
        return 0 if min_value==2001 else min_value

s = Solution()
print(s.flipgame([1,1], [2,1]))