LeetCode in Racket
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:
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.
Solution
(define/contract (recur nums)
(-> (listof exact-integer?) pair?)
(if (empty? nums) (cons 0 -1000000)
(let* ([i (first nums)]
[res (recur (cdr nums))]
[currBest (car res)]
[bestSofar (cdr res)]
[currNew (max i (+ currBest i))]
)
(cons currNew (max bestSofar currNew)))))
(define/contract (max-sub-array nums)
(-> (listof exact-integer?) exact-integer?)
(cdr (recur nums)))