#918 - Maximum Sum Circular Subarray

Problem Description

Given a circular integer array nums of length n, return the maximum possible sum of a non-empty subarray of nums.

A circular array means the end of the array connects to the beginning of the array.

Formally, the next element of nums[i] is nums[(i + 1) % n] and the previous element of nums[i] is nums[(i - 1 + n) % n].

A subarray may only include each element of the fixed buffer nums at most once.

Formally, for a subarray nums[i], nums[i + 1], ..., nums[j], there does not exist i <= k1, k2 <= j with k1 % n == k2 % n.

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var maxSubarraySumCircular = function(nums) {
  let [min, max, sum] = [nums[0], nums[0], nums[0]];

  for (let i = 1, prevMin = nums[0], prevMax = nums[0]; i < nums.length; i++) {
    prevMax = Math.max(nums[i], prevMax + nums[i]);
    max = Math.max(max, prevMax);
    prevMin = Math.min(nums[i], prevMin + nums[i]);
    min = Math.min(min, prevMin);
    sum += nums[i];
  }

  return max > 0 ? Math.max(max, sum - min) : max;
};