commit eeaa0335d156f878e123eff64c983e835d254a2d
parent c420ace3d85d29e8beebe6b58cd84b8f68757810
Author: aabacchus <bvnfuller@gmail.com>
Date: Wed, 8 Dec 2021 17:00:08 +0000
21.3
Diffstat:
| A | 2021/03/3.c | | | 53 | +++++++++++++++++++++++++++++++++++++++++++++++++++++ |
| A | 2021/03/3.scm | | | 79 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
| A | 2021/03/input | | | 1000 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
3 files changed, 1132 insertions(+), 0 deletions(-)
diff --git a/2021/03/3.c b/2021/03/3.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#define WIDTH 12
+
+int
+main(int argc, char **argv) {
+ if (argc < 2) {
+ fprintf(stderr, "usage: %s datafile\n", *argv);
+ return 1;
+ }
+
+ FILE *fd = fopen(argv[1], "r");
+ if (fd == NULL) {
+ perror(argv[1]);
+ return 1;
+ }
+
+ int counts[WIDTH] = {0};
+
+ char *buf = NULL;
+ size_t buflen = 0;
+ int len = 0;
+ while (getline(&buf, &buflen, fd) != -1) {
+ len++;
+ for (int i = 0; i < WIDTH; i++)
+ counts[i] += buf[i] == '1' ? 1 : 0;
+ }
+
+ uint16_t gamma, epsilon;
+ gamma = epsilon = 0;
+
+ for (int i = 0; i < WIDTH; i++) {
+ if (counts[i] > len / 2)
+ gamma |= 1 << (WIDTH - 1 - i);
+ else
+ epsilon |= 1 << (WIDTH - 1 - i);
+ }
+
+ printf("epsilon: %d\ngamma: %d\n", epsilon, gamma);
+ printf("product: %d\n", epsilon * gamma);
+
+ free(buf);
+
+ if (fclose(fd) == EOF) {
+ perror("fclose");
+ return 1;
+ }
+
+ return 0;
+}
diff --git a/2021/03/3.scm b/2021/03/3.scm
@@ -0,0 +1,79 @@
+(import (chicken io)
+ (chicken string)
+ (srfi-151))
+
+(define txtlines (call-with-input-file "input" read-lines))
+(define lines (map string->list txtlines))
+
+(define (transpose matrix)
+ (apply map list matrix))
+
+(define (chars->nums l)
+ (map (lambda (x) (- x 48)) (map char->integer l)))
+
+(define ints (map chars->nums lines))
+
+; return #t or #f so it works with srfi-151's list->bits
+(define (mode-0-1-ind l i)
+ (let ((sum (apply + (map (lambda (xl) (list-ref xl i)) l)))
+ (n (length l)))
+ (if (<= 0.5 (/ sum n))
+ #t
+ #f)))
+
+(define (construct-modes nums)
+ (let loop ((i 0) (lst '()))
+ (if (>= i (length (car nums)))
+ (reverse lst)
+ (loop (+ i 1) (cons (mode-0-1-ind nums i) lst)))))
+
+(define gamma-bitlist (construct-modes ints))
+(define epsilon-bitlist (map not gamma-bitlist))
+
+; reverse because the list is interpreted as least sig bit last
+(define gamma (list->bits (reverse gamma-bitlist)))
+(define epsilon (list->bits (reverse epsilon-bitlist)))
+
+; part 1
+(print (* gamma epsilon))
+
+
+; part 2
+
+; remove-elem returns lst without elements satisfying condit
+(define (remove-elem lst condit)
+ (cond
+ ((null? lst) '())
+ ((condit (car lst)) (remove-elem (cdr lst) condit))
+ (else (cons (car lst) (remove-elem (cdr lst) condit)))))
+
+(define (bool->int b)
+ (unless (boolean? b) (error "not a boolean" b))
+ (if b 1 0))
+
+(define (int->bool i)
+ (unless (integer? i) (error "not an integer" i))
+ (cond ((= 0 i) #f)
+ (else #t)))
+
+; most-or least is a boolean: #t to keep values which are the most common
+(define (remove-not-matching lst index most-or-least)
+ (remove-elem lst
+ (lambda (x)
+ (= (list-ref x index)
+ (bool->int
+ (if most-or-least
+ (not (mode-0-1-ind lst index))
+ (mode-0-1-ind lst index)))))))
+
+; most-or least is a boolean: #t to keep values which are the most common
+(define (find-last-matching lst most-or-least)
+ (let loop ((i 0) (l lst))
+ (cond ((= (length l) 1) (car l))
+ (else (loop (+ i 1) (remove-not-matching l i most-or-least))))))
+
+; reverse because the list is interpreted as least sig bit last
+(define co2 (list->bits (reverse (map int->bool (find-last-matching ints #f)))))
+(define oxy (list->bits (reverse (map int->bool (find-last-matching ints #t)))))
+
+(print (* oxy co2))
diff --git a/2021/03/input b/2021/03/input
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