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#lang racket
(define/contract (maximum-population logs)
(-> (listof (listof exact-integer?)) exact-integer?)
; make a hash table of every year encountered between the birth and death years
(define population (make-hash))
; for each person in the logs,
(for/list ([person (in-list logs)])
; for every year from birth to the year before death,
(for/list ([year (in-range (first person) (second person))])
; look up the year in the hash table and add 1 to its key,
; or add the key and set its value to 1 if it doesn't exist yet
(hash-update! population year add1 1)))
; convert the hash table to a list,
; sort the list by year,
; find the first element that maximizes the count,
; and return the associated year
(car (argmax cdr (sort (hash->list population) < #:key car))))
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