My yearly advent-of-code solutions
treybastian.com
1program day_06_part_2
2 implicit none
3 character(len=130) :: line, lines(130), temp_lines(130)
4 integer:: io, x,y, xd,yd, i, j, ct, o_ct, init_x, init_y, init_xd, init_yd
5
6 open(newunit=io, file='./day_06_input.txt', status='old', action='read')
7 read(io, '(a)') lines
8
9 ct = 0
10 ! find starting position
11 do i = 1, size(lines)
12 if (index(lines(i), '^') > 0) then
13 y = i
14 x = index(lines(i), '^')
15 lines(i)(x:x) = '.' ! replace with a dot to not confuse this part
16 xd = 0
17 yd = -1
18 init_x = x
19 init_y = y
20 init_xd = xd
21 init_yd = yd
22 exit
23 end if
24 end do
25
26 do i = 1, size(lines)
27 do j = 1, len(lines(i))
28 o_ct = 0
29 ! reset positions
30 x = init_x
31 y = init_y
32 xd = init_xd
33 yd = init_yd
34 temp_lines = lines ! fresh board every run
35 if(temp_lines(i)(j:j) == '.') then
36 temp_lines(i)(j:j) = 'O' ! place obstacle to test
37 ! move until we leave the bounds when we hit a valid spot mark it with an X and increase count
38 do
39 ! are we going out of bounds?
40 if (x+xd < 1 .or. x+xd > len(temp_lines(y)) .or. y+yd < 1 .or. y+yd > size(temp_lines)) then
41 exit
42 end if
43
44 ! try to move
45 select case(temp_lines(y+yd)(x+xd:x+xd))
46 case('.')
47 ! valid move
48 x = x + xd
49 y = y + yd
50 case('O')
51 ! we are blocked lets rotate 90 degrees and count obstacle
52 o_ct = o_ct + 1
53 if(xd == 0 .and. yd == -1) then
54 xd = 1
55 yd = 0
56 else if (xd == 1 .and. yd == 0) then
57 xd = 0
58 yd = 1
59 else if (xd == 0 .and. yd == 1) then
60 xd = -1
61 yd = 0
62 else if (xd == -1 .and. yd == 0) then
63 xd = 0
64 yd = -1
65 end if
66 case('#')
67 ! we are blocked lets rotate 90 degrees
68 ! change this to an O to try and detect when stuck
69 temp_lines(y+yd)(x+xd:x+xd) = 'O'
70 if(xd == 0 .and. yd == -1) then
71 xd = 1
72 yd = 0
73 else if (xd == 1 .and. yd == 0) then
74 xd = 0
75 yd = 1
76 else if (xd == 0 .and. yd == 1) then
77 xd = -1
78 yd = 0
79 else if (xd == -1 .and. yd == 0) then
80 xd = 0
81 yd = -1
82 end if
83 case default
84 exit
85 end select
86 if(o_ct > 100) then
87 exit ! probably stuck
88 end if
89 end do
90 end if
91 if(o_ct > 100) then ! we got stuck probably 100 is so arbitrary
92 ct = ct + 1
93 end if
94 end do
95 end do
96 print*, "block points: ", ct
97end program day_06_part_2