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|
package main
import (
"bufio"
"fmt"
"log"
"os"
)
const (
startSquare = 'S'
endSquare = 'E'
)
func byte2height(b byte) int {
return int(b - 'a')
}
type square struct {
x, y, i int
height int
}
type heightmap struct {
squares [][]*square
work []*square
pathlog map[int]*square
distances map[int]int
}
func (h *heightmap) distance(s *square, o *square) int {
return 1
}
func (h *heightmap) neighbors(s *square, pred func(n, s *square) bool) []*square {
potential := []*square{}
if s.x > 0 {
potential = append(potential, h.squares[s.y][s.x-1])
}
if s.x < len(h.squares[0])-1 {
potential = append(potential, h.squares[s.y][s.x+1])
}
if s.y > 0 {
potential = append(potential, h.squares[s.y-1][s.x])
}
if s.y < len(h.squares)-1 {
potential = append(potential, h.squares[s.y+1][s.x])
}
ns := []*square{}
for _, n := range potential {
if pred(n, s) {
ns = append(ns, n)
}
}
return ns
}
func (hm *heightmap) shortestPath(
start *square,
pred func(sqr *square) bool,
neighborPred func(n, s *square) bool,
) ([]*square, bool) {
infinity := len(hm.squares) * len(hm.squares[0])
hm.work = make([]*square, len(hm.squares)*len(hm.squares[0]))
for i := range hm.squares {
for j := range hm.squares[i] {
s := hm.squares[i][j]
hm.distances[s.i] = infinity
hm.pathlog[s.i] = nil
hm.work[j+(i*len(hm.squares[0]))] = s
}
}
hm.distances[start.i] = 0
var sqr *square
for len(hm.work) > 0 {
var i int
sqr = hm.work[0]
for j, sqrmin := range hm.work {
if hm.distances[sqrmin.i] < hm.distances[sqr.i] {
sqr = sqrmin
i = j
}
}
if sqr == nil {
log.Fatal("No min distance square found")
}
hm.work[i], hm.work[len(hm.work)-1] = hm.work[len(hm.work)-1], hm.work[i]
hm.work = hm.work[:len(hm.work)-1]
if pred(sqr) {
break
}
for _, n := range hm.neighbors(sqr, neighborPred) {
d := hm.distances[sqr.i] + hm.distance(sqr, n)
if d < hm.distances[n.i] {
hm.distances[n.i] = d
hm.pathlog[n.i] = sqr
}
}
}
path := []*square{}
if hm.pathlog[sqr.i] == nil {
return path, false
}
ptr := sqr.i
for hm.pathlog[ptr] != nil {
p := hm.pathlog[ptr]
path = append(path, p)
ptr = p.i
}
return path, true
}
func main() {
f, err := os.Open("day12.txt")
if err != nil {
log.Fatal("Could not read input data", err)
}
s := bufio.NewScanner(f)
y := 0
d := make(map[int]int)
hm := &heightmap{
pathlog: make(map[int]*square),
distances: d,
}
var start, end *square
for s.Scan() {
squareRow := make([]*square, len(s.Bytes()))
for x, c := range s.Bytes() {
if c == 'S' {
s := &square{x, y, x + (y * len(s.Bytes())), byte2height('a')}
squareRow[x] = s
start = s
} else if c == 'E' {
s := &square{x, y, x + (y * len(s.Bytes())), byte2height('z')}
squareRow[x] = s
end = s
} else {
s := &square{x, y, x + (y * len(s.Bytes())), byte2height(c)}
squareRow[x] = s
}
}
hm.squares = append(hm.squares, squareRow)
y++
}
p1path, ok := hm.shortestPath(start, func(sqr *square) bool {
return sqr == end
}, func(n, s *square) bool {
return (n.height - s.height) <= 1
})
if ok {
fmt.Println("Part 1:", len(p1path))
}
p2path, ok := hm.shortestPath(end, func(sqr *square) bool {
return sqr.height == byte2height('a')
}, func(n, s *square) bool {
return (s.height - n.height) <= 1
})
if ok {
fmt.Println("Part 2:", len(p2path))
}
}
|
