Card Flipping Game — LeetCode 822 Python Solution

The problem

You are given two 0-indexed integer arrays fronts and backs of length n, where the ith card has the positive integer fronts[i] printed on the front and backs[i] printed on the back. Initially, each card is placed on a table such that the front number is facing up and the other is facing down.

Example

Input

fronts = [1,2,4,4,7], backs = [1,3,4,1,3]

Output

2

Explanation

If we flip the second card, the face up numbers are [1,3,4,4,7] and the face down are [1,2,4,1,3].

Python solution

class Solution:
    def flipgame(self, fronts: List[int], backs: List[int]) -> int:
        s = {a for a, b in zip(fronts, backs) if a == b}
        return min((x for x in chain(fronts, backs) if x not in s), default=0)

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 822. Card Flipping Game is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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