1 files changed, 45 insertions, 0 deletions
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