LeetCode-in-All

739. Daily Temperatures

Medium

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

Example 1:

Input: temperatures = [73,74,75,71,69,72,76,73]

Output: [1,1,4,2,1,1,0,0]

Example 2:

Input: temperatures = [30,40,50,60]

Output: [1,1,1,0]

Example 3:

Input: temperatures = [30,60,90]

Output: [1,1,0]

Constraints:

• 1 <= temperatures.length <= 105
• 30 <= temperatures[i] <= 100

Solution

(define/contract (daily-temperatures temp)
    (-> (listof exact-integer?) (listof exact-integer?))
    (let make-answer
        ([i 0] [temp-rev (reverse temp)] [higher null] [answer null])
        (match temp-rev
            [(cons t temp-rev) (let* (
                [higher
                    (let eliminate<=t ([higher higher]) (match higher
                        [(cons (cons t1 _) higher) #:when (>= t t1) (eliminate<=t higher)]
                        [_ higher]))]
                [a (if (null? higher) 0 (- i (cdar higher)))] )
                (make-answer (add1 i) temp-rev (cons (cons t i) higher) (cons a answer)))]
            [(list) answer])))

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