gistfile1.txt

--- Day 12: Hill Climbing Algorithm ---

You try contacting the Elves using your handheld device, but the river you're following must be too low to get a decent signal.

You ask the device for a heightmap of the surrounding area (your puzzle input). The heightmap shows the local area from above broken into a grid; the elevation of each square of the grid is given by a single lowercase letter, where a is the lowest elevation, b is the next-lowest, and so on up to the highest elevation, z.

Also included on the heightmap are marks for your current position (S) and the location that should get the best signal (E). Your current position (S) has elevation a, and the location that should get the best signal (E) has elevation z.

You'd like to reach E, but to save energy, you should do it in as few steps as possible. During each step, you can move exactly one square up, down, left, or right. To avoid needing to get out your climbing gear, the elevation of the destination square can be at most one higher than the elevation of your current square; that is, if your current elevation is m, you could step to elevation n, but not to elevation o. (This also means that the elevation of the destination square can be much lower than the elevation of your current square.)

For example:

Sabqponm
abcryxxl
accszExk
acctuvwj
abdefghi
Here, you start in the top-left corner; your goal is near the middle. You could start by moving down or right, but eventually you'll need to head toward the e at the bottom. From there, you can spiral around to the goal:

v..v<<<<
>v.vv<<^
.>vv>E^^
..v>>>^^
..>>>>>^
In the above diagram, the symbols indicate whether the path exits each square moving up (^), down (v), left (<), or right (>). The location that should get the best signal is still E, and . marks unvisited squares.

This path reaches the goal in 31 steps, the fewest possible.

What is the fewest steps required to move from your current position to the location that should get the best signal?

gistfile2.txt

abccccccccaaaaaaaccaaaaaaaaaaaaaaaaccccccccccccccccccccccccccccccccccccaaaaaa
abccccccccaaaaaaaccaaaaaaaaaaaaaaaaccccccccccccccccccccccccccccccccccccaaaaaa
abccccccccccaaaaaaccaaaaaaaaaaaaaaaaccccccccccccccccacccccccccccccccccccaaaaa
abcccccaaaacaaaaaaccaaaaaaaaaaaaaaaaacccccccccccccccaaaccccaccccccccccccccaaa
abccccaaaaacaaccccccaaaaaacaaacaacaaaaaaacccccccccccaaaacccaacccccccccccccaaa
abaaccaaaaaaccccaaacaaaacacaaacaaccaaaaaacccccccccccaklaccccccccccccccccccaac
abaaccaaaaaaccaaaaaacccccccaaacccaaaaaaaccccccccccckkkllllccccccccccccccccccc
abaaccaaaaaaccaaaaaacccccccaaaaacaaaaaaacccccccccckkkklllllcccccccaaaccaccccc
abacccccaacccccaaaaacccccccaaaaaccaaaaaaacccccccckkkkpppllllccccccaaaaaaccccc
abacccccccccccaaaaacccccccccaaaacccaaaaaaccccccckkkkpppppplllccccddddaaaccccc
abccccccccccccaaaaaccccccccccaaaccaaaccccccccccckkkppppppppllllldddddddaccccc
abccacccccccccccccccccccccccccccccaaccccccccccckkkopppupppplllmmmmdddddaacccc
abccaaacaaaccccccccccccccccccccaaaaaaaaccccccckkkkopuuuuupppllmmmmmmddddacccc
abccaaaaaaaccccccccccccccccccccaaaaaaaacccccjjkkkooouuuuuuppqqqqqmmmmddddcccc
abccaaaaaacccccccccccccccaaccccccaaaacccccjjjjjjoooouuxuuuppqqqqqqmmmmdddcccc
abcaaaaaaaacccccccccccccaaacccccaaaaaccccjjjjoooooouuuxxuuvvvvvqqqqmmmdddcccc
abaaaaaaaaaacccccccaaaaaaacaacccaacaaacccjjjooooouuuuxxxxvvvvvvvqqqmmmdddcccc
abaaaaaaaaaacccaaacaaaaaaaaaacccacccaaccjjjooootttuuuxxxyyvyyvvvqqqmmmeeecccc
abcccaaacaaacccaaaaaaacaaaaaccccccccccccjjjooottttxxxxxxyyyyyyvvqqqmmmeeccccc
abcccaaacccccccaaaaaacaaaaaccccaaccaacccjjjnnntttxxxxxxxyyyyyvvvqqqnneeeccccc
SbccccaacccccccaaaaaaaaacaaacccaaaaaacccjjjnnntttxxxEzzzzyyyyvvqqqnnneeeccccc
abcccccccccccccaaaaaaaaacaaccccaaaaaccccjjjnnnttttxxxxyyyyyvvvrrrnnneeecccccc
abcccaacccccccaaaaaaaaaccccccccaaaaaacccciiinnnttttxxxyyyyywvvrrrnnneeecccccc
abcccaaaaaaccaaaaaaaacccccccccaaaaaaaaccciiiinnnttttxyyywyyywvrrrnnneeecccccc
abcccaaaaaaccaaaaaaaacccccccccaaaaaaaacccciiinnnntttxwywwyyywwwrrnnneeecccccc
abcaaaaaaaccaaaaaaaaaccccccccccccaacccccccciiinnnttwwwwwwwwwwwwrrnnneeecccccc
abcaaaaaaaccaaaaaacccccccccccccccaaccccccaaiiiinnttwwwwwwwwwwwrrrnnnffecccccc
abcccaaaaaaccaaaaaccccccccccccccccccccaaaaaciiinnssswwwssssrwwrrrnnnfffcccccc
abaacaaccaaccaaaccccccccaacccccccccccccaaaaaiiinnssssssssssrrrrrronnfffcccccc
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abaaaccccaaaaaacccccccaaaaaacccccccccccccaacchhhmmmmmmmmmoooooooooffffaaccccc
abaacccaaaaaaaccccccaaaaaaaaccccaaccccccccccchhhhmmmmmmmgggggooofffffaaaccccc
abaacccaaaaaaaccccccaaaaaaaccccaaaaccccccccccchhhhmmmmhggggggggfffffaaaaccccc
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abccaacccaaaaaaccccccccaaaaaccaaaaacccccccccccchhhhhhhggaaaaaaccccccccccccccc
abccaaaccaaccccccccccccccaaaaaaaaaccccccccccccccchhhhaaaccaaaacccccccccccccaa
abaaaaaaaccccccccccccccccaaaaaaaaccccccccccccccccccccaaaccccaaccccccccccccaaa
abaaaaaaaccccccccaaaccccacaaaaaacccccccccccccccccccccaaaccccccccccccccccccaaa
abaaaaaacccccccaaaaacaaaaaaaaaaacccccccccccccccccccccaaccccccccccccccccaaaaaa
abaaaaaacccccccaaaaaaaaaaaaaaaaaaacccccccccccccccccccccccccccccccccccccaaaaaa