From 6a80d60e44038734f9a5b2a9008f5bb0ea7d65d0 Mon Sep 17 00:00:00 2001
From: Petra <petra@petras.space>
Date: Sun, 3 Dec 2023 20:39:39 +1300
Subject: [PATCH] 2019 Day 4

---
 2019/src/day04.f90 | 114 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 2019/src/day04.f90

diff --git a/2019/src/day04.f90 b/2019/src/day04.f90
new file mode 100644
index 0000000..65e1c12
--- /dev/null
+++ b/2019/src/day04.f90
@@ -0,0 +1,114 @@
+program day3
+    implicit none
+    character(100) :: arg
+    integer :: search_low, search_high
+    integer :: i, num_valid, num_valid2, n_arguments
+    num_valid = 0
+    num_valid2 = 0
+
+    n_arguments = command_argument_count()
+    if (n_arguments .ne. 2) then
+        print *, "Wrong number of arguments: ", n_arguments
+        stop
+    else
+        call get_command_argument(1, arg)
+        read (arg, *) search_low
+        call get_command_argument(2, arg)
+        read (arg, *) search_high
+    end if
+
+    do i=search_low, search_high
+        if ((n_digits(i) .eq. 6) .and. (.not. decreases(i)) .and. (has_duplicate(i))) then
+            num_valid = num_valid + 1
+            if (has_strict_double(i)) then
+                num_valid2 = num_valid2 + 1
+                write(*, 21) num_valid2, i
+            else
+                write(*, 20) num_valid, i
+            end if
+        end if
+    end do
+    write(*, 30) num_valid
+    write(*, 31) num_valid2
+
+20  format('  ', i6, ': ', i6)
+21  format('* ', i6, ': ', i6)
+30  format('Number found for criteria 1: ', i6)
+31  format('Number found for criteria 2: ', i6)
+
+
+    contains
+        function n_digits(val)
+            implicit none
+            integer, intent(in) :: val
+            integer :: n_digits
+            n_digits = floor(log10(real(val))) + 1
+        end function n_digits
+
+        function decreases(val)
+            implicit none
+            integer, intent(in) :: val
+            logical :: decreases
+            integer :: dig, dig_2, n_dig, i, remainder
+            decreases = .false.
+            n_dig = n_digits(val)
+            remainder = val
+            dig = huge(dig)
+            do i = 1,n_dig
+                dig_2 = mod(remainder, 10)
+                remainder = remainder / 10
+                if (dig_2 .gt. dig) then
+                    decreases = .true.
+                    return
+                else
+                    dig = dig_2
+                end if
+            end do
+        end function decreases
+
+        function has_duplicate(val)
+            implicit none
+            integer, intent(in) :: val
+            logical :: has_duplicate
+            integer :: i, dig, dig_2, n_dig, remainder
+            has_duplicate = .false.
+            n_dig = n_digits(val)
+            remainder = val
+            dig = -1
+            do i = 1,n_dig
+                dig_2 = mod(remainder, 10)
+                remainder = remainder / 10
+                if (dig_2 .eq. dig) then
+                    has_duplicate = .true.
+                    return
+                else
+                    dig = dig_2
+                end if
+            end do
+        end function has_duplicate
+
+        function has_strict_double(val) result(hd)
+            implicit none
+            integer, intent(in) :: val
+            logical :: hd
+            integer :: i, dig_1, dig_2, dig_3, dig_4, n_dig, remainder
+            hd = .false.
+            n_dig = n_digits(val)
+            remainder = val
+            dig_1 = -1
+            dig_2 = -2
+            dig_3 = -3
+            do i = 1,n_dig+1
+                dig_4 = mod(remainder, 10)
+                remainder = remainder / 10
+                if ((dig_3 .eq. dig_2) .and. (dig_2 .ne. dig_1) .and. (dig_4 .ne. dig_3)) then
+                    hd = .true.
+                    return
+                else
+                    dig_1 = dig_2
+                    dig_2 = dig_3
+                    dig_3 = dig_4
+                end if
+            end do
+        end function has_strict_double
+end program day3