3 files changed, 187 insertions, 0 deletions
diff --git a/2020/10/part1.c b/2020/10/part1.c
new file mode 100644
index 0000000..f5a700e
--- /dev/null
+++ b/2020/10/part1.c
@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <string.h>
+
+#define MAX_INPUT_LEN 128
+
+void insert_value_sorted(int *list, size_t *size, int value)
+{
+    long long low = 0, high = *size;
+    while (low < high) {
+        int m = low + (high - low) / 2;
+        if (list[m] < value) {
+            low = m + 1;
+        }
+        else if (list[m] > value) {
+            high = m;
+        }
+        else {
+            // Value already exists in the list
+            return;
+        }
+    }
+
+    for (long long i = *size - 1; i >= low; i--) {
+        list[i + 1] = list[i];
+    }
+
+    (*size)++;
+    list[low] = value;
+}
+
+int solve(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[128] = { 0 };
+
+    int input[MAX_INPUT_LEN] = { 0 };
+    size_t input_size = 1; // 0 is our start value
+
+    while (fgets(buffer, 128, file)) {
+        insert_value_sorted(input, &input_size, atoi(buffer));
+    }
+
+    fclose(file);
+
+    int diff1 = 0;
+    int diff3 = 1; // Diff with adapter
+
+    for (size_t i = 1; i < input_size; i++)
+    {
+        int diff = input[i] - input[i - 1];
+        if (diff == 1) {
+            diff1++;
+        }
+        else if (diff == 3) {
+            diff3++;
+        }
+    }
+
+    return diff1 * diff3;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i\n", solve(argv[argc - 1]));
+}
diff --git a/2020/10/part2.c b/2020/10/part2.c
new file mode 100644
index 0000000..5e766d4
--- /dev/null
+++ b/2020/10/part2.c
@@ -0,0 +1,87 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <string.h>
+
+#include "../utils.h"
+
+#define MAX_INPUT_LEN 128
+
+void insert_value_sorted(int *list, size_t *size, int value)
+{
+    long long low = 0, high = *size;
+    while (low < high) {
+        int m = low + (high - low) / 2;
+        if (list[m] < value) {
+            low = m + 1;
+        }
+        else if (list[m] > value) {
+            high = m;
+        }
+        else {
+            // Value already exists in the list
+            return;
+        }
+    }
+
+    for (long long i = *size - 1; i >= low; i--) {
+        list[i + 1] = list[i];
+    }
+
+    (*size)++;
+    list[low] = value;
+}
+
+#ifdef USE_ASM
+uint64_t possible_seq(const int *input, size_t input_size);
+#else
+uint64_t possible_seq(const int *input, size_t input_size)
+{
+    // Use char to optimize for size
+    const static char TRIB[] = { 1, 1, 2, 4, 7 };
+    int con = 0;
+    uint64_t res = 1;
+    const int *prev = input;
+    const int *cur = input + 1;
+    do {
+        if (likely(*cur - *prev == 1)) {
+            con++;
+        }
+        else {
+            res *= TRIB[con];
+            con = 0;
+        }
+    } while (++prev && ++cur < input + input_size);
+
+    return res;
+}
+#endif
+
+uint64_t solve(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[16] = { 0 };
+
+    int input[MAX_INPUT_LEN] = { 0 };
+    size_t input_size = 1; // 0 is our start value
+
+    while (fgets(buffer, 16, file)) {
+        insert_value_sorted(input, &input_size, atoi(buffer));
+    }
+
+    // Add our device's built-in joltage adapter
+    input[input_size] = input[input_size - 1] + 3;
+    input_size++;
+
+    fclose(file);
+
+    return possible_seq(input, input_size);
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%lu\n", solve(argv[argc - 1]));
+}
diff --git a/2020/10/possible_seq.asm b/2020/10/possible_seq.asm
new file mode 100644
index 0000000..b737d13
--- /dev/null
+++ b/2020/10/possible_seq.asm
@@ -0,0 +1,30 @@
+global possible_seq
+
+section .rodata
+    TRIB:   dq 1, 1, 2, 4, 7                ; tribonacci sequence (without first 2 zeroes)
+
+section .text
+
+possible_seq:
+    mov         eax, 1                      ; set up return value
+    xor         ecx, ecx                    ; # of connected elements counter
+    lea         rdx, [rdi + 4 * rsi - 4]    ; pointer to the last element
+    lea         r8, [rel TRIB]
+    jmp         .loop
+.ncon:
+    imul        rax, qword [r8 + 8 * rcx]
+    xor         ecx, ecx
+    add         rdi, 4
+    cmp         rdi, rdx
+    jae         .return
+.loop:
+    mov         esi, dword [rdi + 4]
+    sub         esi, dword [rdi]
+    cmp         esi, 1
+    jne         .ncon
+    inc         ecx
+    add         rdi, 4
+    cmp         rdi, rdx
+    jb          .loop
+.return:
+    ret