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program day_03
implicit none
integer ::io, ios, a, b, state, res, cmd_state, digit_state
character(len=1) :: c
character(len=10) :: buffer ! buffer to store the number
res = 0
open(newunit=io, file='./day_03_input.txt', status='old', action='read', access='stream')
state = 0 ! 0 = find command, 1 = find number, 3 = calculate
digit_state = 0 ! 0 = find a, 1 = find b
cmd_state = 0 ! 0 = find m, 1 = find u, 2 = find l 3 = find (
buffer = ''
do
read(io, iostat=ios) c
if (ios /= 0) exit
select case(state)
case (0) ! find command
select case(cmd_state)
case (0) ! find m
if (c == 'm') then
cmd_state = 1
else
cmd_state = 0
end if
case (1) ! find u
if (c == 'u') then
cmd_state = 2
else
cmd_state = 0
end if
case(2) ! find l
if (c == 'l') then
cmd_state = 3
else
cmd_state = 0
end if
case(3) ! find (
if (c == '(') then
state = 1
cmd_state = 0
else
cmd_state = 0
end if
end select
case (1) ! find digits
select case (iachar(c))
case (48:57) ! 0-9
buffer = trim(buffer) // c
case (44) ! ,
if (digit_state == 0 .and. len(trim(buffer)) > 0) then
read(buffer, *) a
print*, 'a: ', a
buffer = ''
digit_state = 1
else
state = 0 ! invalid
digit_state = 0
buffer = ''
end if
case (41) ! )
if(digit_state == 1 .and. len(trim(buffer)) > 0) then
read(buffer, *) b
print*, 'b: ', b
state = 3 ! reset state
digit_state = 0
buffer = ''
else
state = 0
digit_state = 0
buffer = ''
end if
case default
state = 0
digit_state = 0
buffer = ''
end select
end select
if(state == 3) then
res = res + (a * b)
state = 0
end if
end do
print*, res
end program
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