adding old leetcode solutions

1 files changed, 17 insertions, 0 deletions

diff --git a/leetcode/lc-1854-max-pop-year.rkt b/leetcode/lc-1854-max-pop-year.rkt
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index 0000000..75104f1
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+++ b/leetcode/lc-1854-max-pop-year.rkt
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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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