Hard
You are given an array of integers nums
, there is a sliding window of size k
which is moving from the very left of the array to the very right. You can only see the k
numbers in the window. Each time the sliding window moves right by one position.
Return the max sliding window.
Example 1:
Input: nums = [1,3,-1,-3,5,3,6,7], k = 3
Output: [3,3,5,5,6,7]
Explanation:
Window position Max
[1 3 -1] -3 5 3 6 7 3
1 [3 -1 -3] 5 3 6 7 3
1 3 [-1 -3 5] 3 6 7 5
1 3 -1 [-3 5 3] 6 7 5
1 3 -1 -3 [5 3 6] 7 6
1 3 -1 -3 5 [3 6 7] 7
Example 2:
Input: nums = [1], k = 1
Output: [1]
Constraints:
1 <= nums.length <= 105
-104 <= nums[i] <= 104
1 <= k <= nums.length
(require racket/contract)
(define/contract (max-sliding-window nums k)
(-> (listof exact-integer?) exact-integer? (listof exact-integer?))
(if (= k 1)
nums ; Special case where each window is just a single number
(let* ([n (length nums)]
[nums-vec (list->vector nums)]
[capacity n]
[dq (make-vector capacity 0)]
[head (box 0)]
[tail (box 0)]
[result '()])
;; Helper functions for deque operations
(define (deque-empty?) (= (unbox head) (unbox tail)))
(define (deque-push-back! idx)
(vector-set! dq (unbox tail) idx)
(set-box! tail (modulo (+ (unbox tail) 1) capacity)))
(define (deque-pop-back!)
(set-box! tail (modulo (- (unbox tail) 1) capacity)))
(define (deque-front) (vector-ref dq (unbox head)))
(define (deque-pop-front!)
(set-box! head (modulo (+ (unbox head) 1) capacity)))
(define (deque-back)
(vector-ref dq (if (= (unbox tail) 0) (- capacity 1) (- (unbox tail) 1))))
(define (pop-back-while cur)
(when (not (deque-empty?))
(when (< (vector-ref nums-vec (deque-back)) cur)
(deque-pop-back!)
(pop-back-while cur))))
;; Iterate through nums
(for ([idx (in-range n)])
(let ([cur (vector-ref nums-vec idx)])
(pop-back-while cur)
(deque-push-back! idx)
(when (and (>= idx k)
(not (deque-empty?))
(equal? (deque-front) (- idx k)))
(deque-pop-front!))
(when (>= idx (sub1 k))
(set! result (cons (vector-ref nums-vec (deque-front)) result)))))
(reverse result))))