## DEV Community

Subramanya Chakravarthy

Posted on

# Maximum Points You Can Obtain from Cards - LeetCode

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;
};
``````