LeetCode-in-All

53. Maximum Subarray

Medium

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

defmodule Solution do
  @spec max_sub_array(nums :: [integer]) :: integer
  def max_sub_array([h | t]) do
    solve(t, h, h)
  end

  defp solve([], curr_sum, max_sum), do: max(curr_sum, max_sum)

  defp solve(nums, curr_sum, max_sum) when curr_sum < 0 do
    solve(nums, 0, max_sum)
  end

  defp solve([h | t], curr_sum, max_sum) do
    curr_sum = curr_sum + h
    solve(t, curr_sum, max(curr_sum, max_sum))
  end
end