5 files changed, 335 insertions, 0 deletions
diff --git a/2020/09/part1.c b/2020/09/part1.c
new file mode 100644
index 0000000..d17fb2b
--- /dev/null
+++ b/2020/09/part1.c
@@ -0,0 +1,54 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#define INPUT_LEN 1000
+#define SEARCH_LEN 25
+
+bool has_sum(uint64_t *cur_num)
+{
+    uint64_t search = *cur_num;
+    uint64_t *p1 = cur_num - SEARCH_LEN;
+    do {
+        uint64_t *p2 = cur_num - SEARCH_LEN;
+        do {
+            if (*p1 + *p2 == search) {
+                return true;
+            }
+        } while (++p2 < cur_num);
+    } while (++p1 < cur_num);
+
+    return false;
+}
+
+int exe_program(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[24] = { 0 };
+
+    uint64_t nums[INPUT_LEN];
+    size_t num_size = 0;
+
+    while (fgets(buffer, 24, file)) {
+        nums[num_size++] = strtoull(buffer, NULL, 10);
+    }
+
+    fclose(file);
+
+    uint64_t *cur_num = nums + SEARCH_LEN;
+    do {
+        if (!has_sum(cur_num)) {
+            return *cur_num;
+        }
+    } while (++cur_num < nums + num_size);
+
+    return -1;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i\n", exe_program(argv[argc - 1]));
+}
diff --git a/2020/09/part1.f90 b/2020/09/part1.f90
new file mode 100644
index 0000000..a89ee41
--- /dev/null
+++ b/2020/09/part1.f90
@@ -0,0 +1,45 @@
+integer function has_sum(arg, arr)
+    implicit none
+
+    integer, parameter :: arr_len = 25
+
+    integer (kind=8) :: arg
+    integer (kind=8), dimension(25) :: arr
+    integer :: i, j
+
+    do i = 1, arr_len
+        do j = 1, arr_len
+            if (arr(i) + arr(j) == arg) then
+                has_sum = 1
+                return
+            end if
+        end do
+    end do
+
+    has_sum = 0
+    return
+end function has_sum
+
+program day9
+    implicit none
+
+    integer, parameter :: input_len = 1000
+
+    integer :: has_sum, i, tmp
+    integer (kind=8), dimension(input_len) :: input
+
+    open(10, file='input', status='old')
+    do i = 1, input_len
+        read(10, *) input(i)
+    end do
+    close(10)
+
+    do i = 26, input_len
+        tmp = has_sum(input(i), input(i - 25))
+        if (tmp == 0) then
+            print *, input(i)
+            stop
+        end if
+    end do
+
+end program day9
diff --git a/2020/09/part2.c b/2020/09/part2.c
new file mode 100644
index 0000000..28c335e
--- /dev/null
+++ b/2020/09/part2.c
@@ -0,0 +1,78 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#define INPUT_LEN 1000
+#define SEARCH_LEN 25
+
+bool has_sum(uint64_t *cur_num)
+{
+    uint64_t search = *cur_num;
+    uint64_t *p1 = cur_num - SEARCH_LEN;
+    do {
+        uint64_t *p2 = cur_num - SEARCH_LEN;
+        do {
+            if (*p1 + *p2 == search) {
+                return true;
+            }
+        } while (++p2 < cur_num);
+    } while (++p1 < cur_num);
+
+    return false;
+}
+
+int exe_program(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[24] = { 0 };
+
+    uint64_t nums[INPUT_LEN] = { 0 };
+    size_t num_size = 0;
+
+    while (fgets(buffer, 24, file)) {
+        nums[num_size++] = strtoull(buffer, NULL, 10);
+    }
+
+    fclose(file);
+
+    uint64_t *cur_num = nums + SEARCH_LEN;
+    uint64_t search = -1;
+    do {
+        if (!has_sum(cur_num)) {
+            search = *cur_num;
+            break;
+        }
+    } while (++cur_num < nums + num_size);
+
+    cur_num = nums;
+    do {
+        uint64_t min = __UINT64_MAX__;
+        uint64_t max = 0;
+        uint64_t sum = 0;
+        uint64_t *p1 = cur_num;
+        do {
+            if (*p1 < min) {
+                min = *p1;
+            }
+            else if (*p1 > max) {
+                max = *p1;
+            }
+
+            sum += *p1;
+
+            if (sum == search) {
+                return min + max;
+            }
+        } while (++p1 < nums + num_size);
+    } while (++cur_num < nums + num_size);
+
+    return -1;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i\n", exe_program(argv[argc - 1]));
+}
diff --git a/2020/09/part2.f90 b/2020/09/part2.f90
new file mode 100644
index 0000000..b7e65de
--- /dev/null
+++ b/2020/09/part2.f90
@@ -0,0 +1,60 @@
+integer function has_sum(arg, arr)
+    implicit none
+
+    integer, parameter :: arr_len = 25
+
+    integer (kind=8) :: arg
+    integer (kind=8), dimension(25) :: arr
+    integer :: i, j
+
+    do i = 1, arr_len
+        do j = 1, arr_len
+            if (arr(i) + arr(j) == arg) then
+                has_sum = 1
+                return
+            end if
+        end do
+    end do
+
+    has_sum = 0
+    return
+end function has_sum
+
+program day9
+    implicit none
+
+    integer, parameter :: input_len = 1000
+
+    integer :: has_sum, i, j, tmp
+    integer (kind=8), dimension(input_len) :: input
+    integer (kind=8) :: search = -1, sum
+
+    open(10, file='input', status='old')
+    do i = 1, input_len
+        read(10, *) input(i)
+    end do
+    close(10)
+
+    do i = 26, input_len
+        tmp = has_sum(input(i), input(i - 25))
+        if (tmp == 0) then
+            search = input(i)
+            exit
+        end if
+    end do
+
+    do i = 1, input_len
+        sum = 0
+        do j = i, input_len
+            sum = sum + input(j)
+            if (sum >= search) then
+                exit
+            end if
+        end do
+        if (sum == search) then
+            print *, minval(input(i:j)) + maxval(input(i:j))
+            stop
+        end if
+    end do
+
+end program day9
diff --git a/2020/09/part2_fast.c b/2020/09/part2_fast.c
new file mode 100644
index 0000000..cf06bbd
--- /dev/null
+++ b/2020/09/part2_fast.c
@@ -0,0 +1,98 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#define INPUT_LEN 1000
+#define SEARCH_LEN 25
+
+uint64_t min_uint64(const uint64_t *start, const uint64_t *stop)
+{
+    uint64_t min = *start;
+    while (++start <= stop) {
+        if (*start < min) {
+            min = *start;
+        }
+    }
+
+    return min;
+}
+
+uint64_t max_uint64(const uint64_t *start, const uint64_t *stop)
+{
+    uint64_t max = *start;
+    while (++start <= stop) {
+        if (*start > max) {
+            max = *start;
+        }
+    }
+
+    return max;
+}
+
+bool has_sum(uint64_t *cur_num)
+{
+    uint64_t search = *cur_num;
+    uint64_t *p1 = cur_num - SEARCH_LEN;
+    do {
+        if (*p1 >= search)
+        {
+            continue;
+        }
+
+        uint64_t *p2 = cur_num - SEARCH_LEN;
+        do {
+            if (*p1 + *p2 == search) {
+                return true;
+            }
+        } while (++p2 < cur_num);
+    } while (++p1 < cur_num);
+
+    return false;
+}
+
+int exe_program(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[24] = { 0 };
+
+    uint64_t nums[INPUT_LEN] = { 0 };
+    size_t num_size = 0;
+
+    while (fgets(buffer, 24, file)) {
+        nums[num_size++] = strtoull(buffer, NULL, 10);
+    }
+
+    fclose(file);
+
+    uint64_t *cur_num = nums + SEARCH_LEN;
+    uint64_t search = -1;
+    do {
+        if (!has_sum(cur_num)) {
+            search = *cur_num;
+            break;
+        }
+    } while (++cur_num < nums + num_size);
+
+    cur_num = nums;
+    do {
+        uint64_t sum = 0;
+        uint64_t *p1 = cur_num;
+        do {
+            sum += *p1;
+        } while (++p1 < nums + num_size && sum < search);
+
+        if (sum == search) {
+            return min_uint64(cur_num, p1) + max_uint64(cur_num, p1);
+        }
+    } while (++cur_num < nums + num_size);
+
+    return -1;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i\n", exe_program(argv[argc - 1]));
+}