The question is a bit tricky, In programming terms we need to find sub-array such that you can draw maximum points

Sliding winndow algorithm is a useful technique whenever you need to find some substring or subarray. Here we need to find a subarray from the beginning and end

Explanation:

example: cardPoints = [1,2,3,4,5,6,1] k = 3

  1. [1,2,3,4,5,6,1] –> start = [1,2,3], end = [], max = 6
  2. [1,2,3,4,5,6,1] –> start = [1,2], end = [1], max = 6
  3. [1,2,3,4,5,6,1] –> start = [1], end = [6, 1], max = 8
  4. [1,2,3,4,5,6,1] –> start = [], end = [5, 6, 1], max = 12

Here’s the algorithm

  1. Create these variables

    • leftWindow = k - 1 , wondering why leftWindow is k - 1? it’s because we need array indices values
    • leftSum = 0

    • rightWindow = cardPoints.length - 1

    • rightSum = 0

  2. Now Loop through the card array k times and add each value to the leftSum

  3. Let’s assume leftSum is the maxSum max = leftSum

  4. Start sliding the window while leftWindow is > 0 then decrease the leftSum and increase the rightSum. check whether leftSum + rightSum is greater than max

Here’s the solution

var maxScore = function(cardPoints, k) {
	let leftW = k - 1, 
		leftSum = 0, 
		rightW = cardPoints.length - 1, 
		rightSum = 0;

	for(let i = 0; i < k; i++) {
		leftSum += cardPoints[i];
	}

	let max = leftSum;

	while(leftW >= 0) {
		leftSum -= cardPoints[leftW];
		rightSum += cardPoints[rightW];

		leftW--;
		rightW--;

		max = Math.max(max, leftSum + rightSum);
	}

	return max;
};

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