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Challenges

Connect the corners without 4 in a row

+2
−0

Connect opposite corners of a rectangle of characters without putting 4 characters in a row.

Input

  • Two numbers, W and H, representing the width and height of the rectangle
  • Each number will be in the range 2 to 70

Output

  • A rectangular grid of characters, of width W and height H
  • You may choose any 2 distinct characters to represent path and background
  • The output must contain 2 connected path characters in diagonally opposite corners of the grid
    • Connected means there is a path from one to the other moving only between adjacent path characters
    • Adjacent means 1 character away horizontally or vertically (but not both - diagonal adjacency does not count as connection for this challenge)
  • The output must not contain 4 adjacent path characters in a line horizontally or vertically
  • There is no limit to how many of the characters may be path characters, provided there are never 4 in a row.
    • There may be redundant sections connected to the path
    • There may be disconnected sections of path provided the main path meets the requirements

Examples

These examples use # for a path character and . for the background.

Valid examples for input 4, 3

##..
.##.
..##

.###
.#..
##..

#...
##..
.###

##.#
.###
##.#

Invalid examples for input 4, 3

4 in a line horizontally:

#...
####
...#

Depends on diagonal adjacency, which does not count as connection:

#...
.#..
..##

Does not connect diagonally opposite corners:

###.
..##
###.

Valid examples for input 7, 5

###....
..#....
..###..
....#..
....###

##.....
.##....
..##...
...##..
....###

#......
#......
##.###.
.#.#.##
.###..#

###....
..###..
###.###
#...#.#
###...#

Invalid examples for input 7, 5

Does not connect two diagonally opposite corners:

###....
..###..
....###
...##..
...#...

Has 4 in a row horizontally:

####...
...#...
...###.
.....#.
.....##

Has 4 in a row vertically:

###....
..#....
..#.###
..###.#
......#

Depends on diagonal adjacency, which does not count as connection:

##.....
..##...
....##.
......#
......#

Validator

You can check a specific output using this path validator, which will give a reason for any failed validations.

Explanations are optional, but I'm more likely to upvote answers that have one.

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1 answer

+2
−0

Haskell + hgl, 134 bytes

k=cy"X.XX"
x#1=[4,0,9,9]!x
2#y=8
3#y=[8,9,4,4]!y
x#3=[0,3]!x
_#_=0
x?y|(n,j)<-fvD 4$x%4#(y%4)=tk y$dr j$tk x<dr n<cy[dr2 k,k,cy".X",k]

Attempt This Online!

I first set up a pretty dense background pattern which doesn't break any rules:

XXX.XXX.XXX.XXX.XXX.
X.XXX.XXX.XXX.XXX.XX
.X.X.X.X.X.X.X.X.X.X
X.XXX.XXX.XXX.XXX.XX
XXX.XXX.XXX.XXX.XXX.
X.XXX.XXX.XXX.XXX.XX
.X.X.X.X.X.X.X.X.X.X
X.XXX.XXX.XXX.XXX.XX
XXX.XXX.XXX.XXX.XXX.
X.XXX.XXX.XXX.XXX.XX
.X.X.X.X.X.X.X.X.X.X
X.XXX.XXX.XXX.XXX.XX
XXX.XXX.XXX.XXX.XXX.
X.XXX.XXX.XXX.XXX.XX
.X.X.X.X.X.X.X.X.X.X
X.XXX.XXX.XXX.XXX.XX
XXX.XXX.XXX.XXX.XXX.
X.XXX.XXX.XXX.XXX.XX
.X.X.X.X.X.X.X.X.X.X
X.XXX.XXX.XXX.XXX.XX

All we have to do is make sure the pattern is aligned so there's always a path. I wish I had some clever way of doing this, but I just use a bunch of magic numbers I calculated by trial and error.

Since the pattern repeats with period 4, I just tried every pair of numbers on the range 1-4 and found a shifting that lined up. I encoded these in base 4 and that's what the program uses.

There might be an opportunity to optimize this by finding better numbers.

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1 comment thread

Occasional misalignment (2 comments)

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