LeetCode-in-All

53. Maximum Subarray

Easy

Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

A subarray is a contiguous part of an array.

Example 1:

Input: nums = [-2,1,-3,4,-1,2,1,-5,4]

Output: 6

Explanation: [4,-1,2,1] has the largest sum = 6.

Example 2:

Input: nums = [1]

Output: 1

Example 3:

Input: nums = [5,4,-1,7,8]

Output: 23

Constraints:

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.

Solution

# @param {Integer[]} nums
# @return {Integer}
def max_sub_array(nums)
  sum_so_far = 0
  max_sum = -Float::INFINITY
  end_ptr = 0

  while end_ptr < nums.length
    sum_so_far += nums[end_ptr]
    max_sum = [max_sum, sum_so_far].max
    sum_so_far = 0 if sum_so_far < 0

    end_ptr += 1
  end

  max_sum
end