maxsubarray.js

function maxSubarrayCrossingSum(arr, left, right, mid) {
  let leftSum = -Infinity;
  let currentSum = 0;

  for (let i = mid; i >= left; i--) {
    currentSum += arr[i];
    if (currentSum > leftSum) leftSum = currentSum;
  }

  let rightSum = -Infinity;
  currentSum = 0;

  for (let i = mid + 1; i <= right; i++) {
    currentSum += arr[i];
    if (currentSum > rightSum) rightSum = currentSum;
  }

  return leftSum + rightSum;
}

function maxSubarraySum(arr, left, right) {
  if (left === right) return arr[left];
  const mid = Math.floor((left + right) / 2);
  return Math.max(
    Math.max(maxSubarraySum(arr, left, mid), maxSubarraySum(arr, mid + 1, right)),
    maxSubarrayCrossingSum(arr, left, right, mid)
  );
}

const a1= [1, -2, 3, 10, -4, 7, 2, -5];
const a2 = [-1, -2, -3, -4, -5];
const a3 = [4, 2, 2, 1, 5, 3];

console.log(maxSubarraySum(a1,0,a1.length-1));
console.log(maxSubarraySum(a2,0,a2.length-1));
console.log(maxSubarraySum(a3,0,a3.length-1));