aoc-2020-10

'AoC-2020, day 10
DIM n(100) AS LONG
OPEN "C:\day10.txt" FOR INPUT AS #1
'OPEN "C:\test10.txt" FOR INPUT AS #1
nums = 0: WHILE NOT EOF(1): nums = nums + 1: INPUT #1, n(nums): WEND

'ynzesort the list
FOR i = 1 TO nums - 1
  FOR j = i + 1 TO nums
    IF n(i) > n(j) THEN temp = n(i): n(i) = n(j): n(j) = temp
  NEXT
NEXT
max = n(nums): nums = nums + 1: n(nums) = max + 3

'compute distances
FOR i = 1 TO nums
  d = n(i) - n(i - 1)
  IF d = 1 THEN d1 = d1 + 1
  IF d = 3 THEN d3 = d3 + 1
NEXT
PRINT "pt1:"; d1; " * "; d3; " = "; d1 * d3

'count paths to the end from each node, starting from the end node and working back
'for each node the number of paths is simply the sum of paths, of each node within reach
DIM c(100) AS _INTEGER64
FOR i = nums TO 0 STEP -1
  IF n(i) = max + 3 THEN c(i) = 1
  FOR j = 1 TO 3
    IF i + j <= nums THEN
      IF n(i + j) - n(i) <= 3 THEN c(i) = c(i) + c(i + j)
    END IF
  NEXT
NEXT
PRINT "pt2:"; c(0)