LeetCode 1423: Maximum Points You Can Obtain from Cards

Meta Data

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Difficulty: medium First Attempt: 2025-12-24

• Submissions: Accepted (first try)

Approach

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Cards come only from the front or back, so after taking k, what remains is always a contiguous middle of n - k cards.

So the maximum taken = total − the minimum sum of a contiguous subarray of length n - k, found with a fixed-size sliding window.

My Solution

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class Solution:
    def maxScore(self, cardPoints: List[int], k: int) -> int:
        n = len(cardPoints)
        size = n - k                               # cards left behind
        window = sum(cardPoints[:size])
        smallest = window
        for right in range(size, n):
            window += cardPoints[right] - cardPoints[right - size]
            smallest = min(smallest, window)
        return sum(cardPoints) - smallest

With k == n, size = 0, the window stays 0, and the answer is the total.

Complexity

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Time O(n), space O(1).

Mistakes to Avoid

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• Greedily taking the larger end each time: earlier picks change what is available later, so it is not always optimal.

Interview Explanation

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Taking k cards from the ends leaves a contiguous middle of n - k cards. So I find the minimum sum of a length-n - k subarray with a fixed sliding window, and the answer is the total minus that. Time O(n).