Add lab 5 content

journal/_src/posts/2022-09-26-lab-five.md

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+    Title: lab-five
+    Date: 2022-09-26T08:30:00
+    Tags: cs2613, lab, racket, recursion, pattern-matching
+
+In this lab I learned about tail end recursion and attempted pattern matching
+
+<!-- more -->
+
+## Tail end recursion
+
+I learned about tail end recursion and how this is way more efficient on the stack, and that racket has certain guarantees about the efficiency of tail end recursion
+
+## Pattern matching
+It was hard for me to see how to utilize pattern matching. I am sure after spending more time with it on the assignment I will be able to figure it out.

labs/L05/count-odds.rkt

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+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(define (count-odds lst)
+  (cond
+    [(empty? lst) 0]
+    [(odd? (first lst)) (add1 (count-odds (rest lst)))]
+    [else (count-odds (rest lst))]))
+
+(module+ test
+  (check-equal? (count-odds (list 3 2 1 1 2 3 4 5 5 6)) 6))
+
+(define (count-odds2 lst)
+  (define (helper lst odds)
+    (cond
+      [(empty? lst) odds]
+      [(odd? (first lst)) (helper (rest lst) (add1 odds))]
+      [else (helper (rest lst) odds)]))
+  (helper lst 0))
+
+(module+ test
+  (check-equal? (count-odds2 (list 3 2 1 1 2 3 4 5 5 6)) 6)
+  (define random-list (build-list 100 (lambda (x) (random 1 100))))
+  (check-equal? (count-odds random-list) (count-odds2 random-list)))
+
+(define (count-odds3 lst)
+  (for/fold
+      ([odds 0])
+      ([n lst])
+    (cond
+      [(odd? n) (add1 odds)]
+      [else odds])))
+
+(module+ test
+  (check-equal? (count-odds3 (list 3 2 1 1 2 3 4 5 5 6)) 6)
+  (check-equal? (count-odds random-list) (count-odds3 random-list))
+  (check-equal? (count-odds3 (list 3 2 1 1 2 3 4 5 5 6)) 6))
+
+(define big-list (range 50000000))
+(for* ([fun (list count-odds count-odds2 count-odds3)]
+       [rep '(1 2 3)])
+  (printf "~a ~a\n" fun rep)
+  (time  (fun big-list)))
+
+;#<procedure:count-odds> 1
+;cpu time: 22109 real time: 22390 gc time: 15828
+;#<procedure:count-odds> 2
+;cpu time: 19578 real time: 19679 gc time: 16250
+;#<procedure:count-odds> 3
+;cpu time: 18109 real time: 18231 gc time: 14859
+;#<procedure:count-odds2> 1
+;cpu time: 3125 real time: 3178 gc time: 93
+;#<procedure:count-odds2> 2
+;cpu time: 2765 real time: 2822 gc time: 31
+;#<procedure:count-odds2> 3
+;cpu time: 2765 real time: 2798 gc time: 31
+;#<procedure:count-odds3> 1
+;cpu time: 1000 real time: 1002 gc time: 0
+;#<procedure:count-odds3> 2
+;cpu time: 1187 real time: 1252 gc time: 15
+;#<procedure:count-odds3> 3
+;cpu time: 984 real time: 1002 gc time: 0

labs/L05/match-ex.rkt

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+#lang racket
+
+
+(define (list-length2 rst)
+(match lst
+  ['() 0]
+  [(list fst rst ...) (add1 (list-length2 rst))]))
+
+(define (list-length3 lst)
+(match lst
+  ['() 0]
+  [(cons fst rst) (add1 list-length3 rst)]))
+

labs/L05/match.rkt

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+#lang racket
+
+(define (list-length list)
+  (match list
+    [`() 0]
+    [(cons head tail) (cons (f head)
+                            (list-length f tail))]))
+
+(module+ test
+    (require rackunit)
+    (check-equal? (list-length '(1 2 3)) 3)
+    (check-equal? (list-length '()) 0))
+
+(define (my-map2 f lst)
+  (match lst
+    ['() '()]
+    [(list head tail ...) (cons (f head)
+                                (my-map2 f tail))]))