130 lines
2.4 KiB
Go
130 lines
2.4 KiB
Go
package main
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import (
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"bufio"
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_ "embed"
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"fmt"
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"strconv"
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"strings"
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aoc "go.sour.is/advent-of-code"
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"golang.org/x/exp/maps"
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)
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// var log = aoc.Log
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func main() { aoc.MustResult(aoc.Runner(run)) }
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type result struct {
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valuePT1 int
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valuePT2 int
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}
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func (r result) String() string { return fmt.Sprintf("%#v", r) }
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func run(scan *bufio.Scanner) (*result, error) {
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var vecsPT1 []vector
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var vecsPT2 []vector
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for scan.Scan() {
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text := scan.Text()
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if len(text) == 0 {
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continue
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}
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v, color := fromLine(text)
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vecsPT1 = append(vecsPT1, v)
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vecsPT2 = append(vecsPT2, fromColor(color))
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}
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return &result{
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valuePT1: findArea(vecsPT1),
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valuePT2: findArea(vecsPT2),
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}, nil
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}
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type vector struct {
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offset point
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scale int
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}
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type point [2]int
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func (p point) add(a point) point {
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return point{p[0] + a[0], p[1] + a[1]}
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}
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func (p point) scale(m int) point {
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return point{p[0] * m, p[1] * m}
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}
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// numPoints the number of the points inside an outline plus the number of points in the outline
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func numPoints(outline []point, borderLength int) int {
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// shoelace - find the float area in a shape
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sum := 0
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for _, p := range pairwise(outline) {
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row1, col1 := p[0][0], p[0][1]
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row2, col2 := p[1][0], p[1][1]
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sum += row1*col2 - row2*col1
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}
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area := sum / 2
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// pick's theorem - find the number of points in a shape given its area
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return (aoc.ABS(area) - borderLength/2 + 1) + borderLength
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}
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func pairwise[T any](arr []T) [][2]T {
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var pairs [][2]T
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for i := range arr[:len(arr)-1] {
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pairs = append(pairs, [2]T{arr[i], arr[i+1]})
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}
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return pairs
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}
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var OFFSET = map[string]point{
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"R": {0, 1},
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"D": {1, 0},
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"L": {0, -1},
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"U": {-1, 0},
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}
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var OFFSET_INDEXES = maps.Values(OFFSET)
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func fromLine(text string) (vector, string) {
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v := vector{}
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s, text, _ := strings.Cut(text, " ")
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v.offset = OFFSET[s]
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s, text, _ = strings.Cut(text, " ")
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v.scale = aoc.Atoi(s)
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_, text, _ = strings.Cut(text, "(#")
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s, _, _ = strings.Cut(text, ")")
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return v, s
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}
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func fromColor(c string) vector {
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scale, _ := strconv.ParseInt(c[:5], 16, 64)
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offset := OFFSET_INDEXES[c[5]-'0']
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return vector{
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offset: offset,
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scale: int(scale),
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}
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}
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func findArea(vecs []vector) int {
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shoelace := []point{{0,0}}
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borderLength := 0
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for _, vec := range vecs {
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scaled_offset := vec.offset.scale(vec.scale)
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shoelace = append(shoelace, shoelace[len(shoelace)-1].add(scaled_offset))
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borderLength += vec.scale
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}
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return numPoints(shoelace, borderLength)
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}
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