day 3 part 1

day3.c

@@ -0,0 +1,101 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <arpa/inet.h>
+
+#define INPUT "inputs/input-day3"
+
+#define BIT_CHECK(v, n) (v >> n) & 1U
+#define BIT_SET(v, n) (v |= 1U << n)
+
+void
+print_bits(uint16_t v, int max)
+{
+    for(int i = 0; i < max; ++i) {
+        printf("%d", BIT_CHECK(v, i));
+    }
+    printf("\n");
+}
+
+uint16_t
+from_bits(char *bits)
+{
+    uint16_t val = 0;
+
+    for(int i = 0; i < 12; ++i) {
+        if(bits[i] == '1') {
+            BIT_SET(val, i);
+        }
+    }
+
+    return val;
+}
+
+int
+count_lines()
+{
+    int total = 0;
+    static char buf[256];
+    FILE *f = fopen(INPUT, "r");
+    while(fgets(buf, 256, f))
+        total++;
+    fclose(f);
+    return total;
+}
+
+uint16_t*
+load_all(int count)
+{
+    uint16_t *i = calloc(sizeof(uint16_t), count);
+
+    int idx = 0;
+    static char buf[256];
+    FILE *f = fopen(INPUT, "r");
+
+    while(fgets(buf, 256, f)) {
+        i[idx] = from_bits(buf);
+        idx++;
+    }
+
+    fclose(f);
+
+    return i;
+}
+
+int
+main()
+{
+    int cnt = count_lines();
+    uint16_t *v = load_all(cnt);
+
+    uint16_t gamma = 0;
+    uint16_t epsilon = 0;
+
+    for(int z = 0; z < 12; ++z) {
+        int high = 0;
+        int low = 0;
+        for(int i = 0; i < cnt; ++i) {
+            int bit = BIT_CHECK(v[i], z);
+            if(bit) {
+                high++;
+            } else {
+                low++;
+            }
+        }
+        if(high > low) {
+            BIT_SET(gamma, (11-z));
+        } else {
+            BIT_SET(epsilon, (11-z));
+        }
+    }
+
+    printf("gamma: %d\nepsilon: %d\n", gamma, epsilon);
+    print_bits(gamma, 16);
+    print_bits(epsilon, 16);
+    printf("result: %d\n", gamma * epsilon);
+
+    free(v);
+    
+    return 0;
+}

makefile

@@ -1,5 +1,5 @@
 
-DAYS = day1 day2
+DAYS = day1 day2 day3
 
 CFLAGS = -Wall -Werror
 

run_all.sh

@@ -1,9 +1,11 @@
 #!/bin/sh
 
-DAYS="day1 day2"
+DAYS="day1 day2 day3"
 
 for x in $DAYS; do
     echo "running" $x
     ./$x
     echo "complete"
-done
+done
+
+exit