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#lang racket
;; https://leetcode.com/problems/two-sum/description/
(define/contract (two-sum nums target)
(-> (listof exact-integer?) exact-integer? (listof exact-integer?))
(define h (make-hash))
(define (loop nums index)
(define n (car nums))
(define diff (- target n))
(if (hash-has-key? h diff)
(list index (hash-ref h diff))
(let ()
(hash-set! h n index)
(loop (cdr nums) (+ 1 index)))))
(loop nums 0))
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