LeetCode in Racket

46. Permutations

Medium

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Example 1:

Input: nums = [1,2,3]

Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Example 2:

Input: nums = [0,1]

Output: [[0,1],[1,0]]

Example 3:

Input: nums = [1]

Output: [[1]]

Constraints:

• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

Solution

(define/contract (permute nums)
  (-> (listof exact-integer?) (listof (listof exact-integer?)))
  (cond [(empty? nums) (list empty)]
        [else (for/fold ([l empty])([i nums])
    (append (map (lambda (lst) (cons i lst)) (permute (remove i nums))) l)
    )
  ]))

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