leetcode 822. Card Flipping Game

leetcode 822. Card Flipping Game

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原题地址：https://leetcode.com/problems/card-flipping-game/

题目

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.

python代码

class Solution:
    def flipgame(self, fronts, backs):
        """
        :type fronts: List[int]
        :type backs: List[int]
        :rtype: int
        """
        all_cards = set(fronts + backs)
        a = {fronts[i] for i in range(len(fronts)) if fronts[i]==backs[i]}
        all_cards = all_cards - a

        return min(all_cards) if all_cards else 0

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