maximumSubarray.js

/*
https://leetcode.com/problems/maximum-subarray/description/

Given an integer array nums, find the subarray with the largest sum, and return its sum.

Example 1:
Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
Output: 6
Explanation: The subarray [4,-1,2,1] has the largest sum 6.

Example 2:
Input: nums = [1]
Output: 1
Explanation: The subarray [1] has the largest sum 1.

Example 3:
Input: nums = [5,4,-1,7,8]
Output: 23
Explanation: The subarray [5,4,-1,7,8] has the largest sum 23.
 
Constraints:
1 <= nums.length <= 105
-104 <= nums[i] <= 104
 
Follow up: If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.
*/

const maxSubArray = (nums) => {
    let largestSum = -Infinity;
    let currentSum = 0;
    let hasReachedZero = false;

    for (const num of nums) {
        if (currentSum + num < 0) {
            currentSum = num;
        } else {
            currentSum += num;
        }
        
        if (!hasReachedZero && currentSum >= 0) {
            hasReachedZero = true;
        }

        if (hasReachedZero) {
            currentSum = Math.max(0, currentSum);
        }

        largestSum = Math.max(largestSum, currentSum);
    }

    return largestSum;
}

module.exports = { maxSubArray };