re-organise repo

2022/go/day09/day09.go

@@ -0,0 +1,119 @@
+package day09
+
+import (
+	"strings"
+
+	"adventofcode2022/utils"
+	sparsegrid "adventofcode2022/utils/sparseGrid"
+)
+
+type rope struct {
+	size int
+	posX []int
+	posY []int
+}
+
+func Part1(input string) int {
+	rope := newRope(2)
+	grid := sparsegrid.NewGrid(false)
+	grid.Set(rope.posX[rope.size-1], rope.posY[rope.size-1], true)
+	for _, line := range strings.Split(input, "\n") {
+		dx := 0
+		dy := 0
+		switch line[0] {
+		case 'R':
+			dx = 1
+		case 'U':
+			dy = -1
+		case 'D':
+			dy = 1
+		case 'L':
+			dx = -1
+		}
+		n := utils.MustAtoi(line[2:])
+		for i := 0; i < n; i++ {
+			// move head
+			rope.posX[0] += dx
+			rope.posY[0] += dy
+
+			// update tail
+			rope.updateTail()
+			grid.Set(rope.posX[rope.size-1], rope.posY[rope.size-1], true)
+		}
+	}
+	return grid.Visited()
+}
+
+func Part2(input string) int {
+	rope := newRope(10)
+	grid := sparsegrid.NewGrid(false)
+	grid.Set(rope.posX[rope.size-1], rope.posY[rope.size-1], true)
+	for _, line := range strings.Split(input, "\n") {
+		dx := 0
+		dy := 0
+		switch line[0] {
+		case 'R':
+			dx = 1
+		case 'U':
+			dy = -1
+		case 'D':
+			dy = 1
+		case 'L':
+			dx = -1
+		}
+		n := utils.MustAtoi(line[2:])
+		for i := 0; i < n; i++ {
+			// move head
+			rope.posX[0] += dx
+			rope.posY[0] += dy
+
+			// update tail
+			rope.updateTail()
+			grid.Set(rope.posX[rope.size-1], rope.posY[rope.size-1], true)
+		}
+	}
+	return grid.Visited()
+}
+
+func newRope(size int) *rope {
+	return &rope{
+		size: size,
+		posX: make([]int, size),
+		posY: make([]int, size),
+	}
+}
+
+func (r *rope) updateTail() {
+outer:
+	for i := 1; i < r.size; i++ {
+		diffX := utils.Abs(r.posX[i-1] - r.posX[i])
+		diffY := utils.Abs(r.posY[i-1] - r.posY[i])
+		if diffX <= 1 && diffY <= 1 {
+			// no need to update node if it's touching
+			continue
+		}
+		moves := [][]int{{1, 0}, {-1, 0}, {0, 1}, {0, -1}}
+		for _, move := range moves {
+			t := utils.Max(
+				utils.Abs(r.posX[i-1]-r.posX[i]+move[0]),
+				utils.Abs(r.posY[i-1]-r.posY[i]+move[1]))
+			if t == 1 {
+				r.posX[i] = r.posX[i-1] + move[0]
+				r.posY[i] = r.posY[i-1] + move[1]
+				continue outer
+			}
+		}
+		moves = [][]int{{1, 1}, {-1, 1}, {1, -1}, {-1, -1}}
+		for _, move := range moves {
+			t := utils.Max(
+				utils.Abs(r.posX[i-1]-r.posX[i]+move[0]),
+				utils.Abs(r.posY[i-1]-r.posY[i]+move[1]))
+			if t == 1 {
+				r.posX[i] = r.posX[i-1] + move[0]
+				r.posY[i] = r.posY[i-1] + move[1]
+				continue outer
+			}
+		}
+		panic("unreachable")
+	}
+}