2021 - Day 15

2021/15/go.mod

@@ -0,0 +1,9 @@
+module AoC/2021/15
+
+require AoC/2021/common v0.0.0
+
+require github.com/joho/godotenv v1.4.0 // indirect
+
+replace AoC/2021/common v0.0.0 => ../common
+
+go 1.17

2021/15/go.sum

@@ -0,0 +1,2 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=

2021/15/main.go

@@ -0,0 +1,224 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"fmt"
+	"sort"
+	"strconv"
+)
+
+type Coord struct {
+	x int;
+	y int;
+}
+
+func printGrid(grid [][]int) {
+	for y := range grid {
+		for _, c := range grid[y] {
+			if c == 10000000 {
+				fmt.Print("--- ")
+			} else {
+				fmt.Printf("%3d ", c)
+			}
+		}
+		fmt.Print("\n")
+	}
+} 
+
+func printSolution(weights [][]int) {
+	current := Coord{len(weights[0])-1, len(weights)-1}
+
+	route := make([][]string, len(weights))
+	for i := range weights {
+		row := make([]string, len(weights[i]))
+		for j := range row {
+			row[j] = "."
+		}
+		route[i] = row
+	}
+
+	route[current.y][current.x] = "x"
+
+	value := 10000000
+	for !(current.x == 0 && current.y == 0) {
+		neighbours := [4]Coord{{current.x+1, current.y}, {current.x-1, current.y}, {current.x, current.y+1}, {current.x, current.y-1}}
+		for _, neighbour := range neighbours {
+			if neighbour.y < 0 || neighbour.y >= len(weights) || neighbour.x < 0 || neighbour.x >= len(weights[neighbour.y]) {
+				continue
+			}
+
+			if weights[neighbour.y][neighbour.x] < value {
+				value = weights[neighbour.y][neighbour.x]
+				current = neighbour
+			}
+		}
+
+		route[current.y][current.x] = "#"
+	}
+
+	route[0][0] = "x"
+
+	for y := range route {
+		for _, c := range route[y] {
+			fmt.Printf("%s", c)
+		}
+		fmt.Printf("\n")
+	}
+}
+
+func updateWeights(grid [][]int, weights [][]int, visited [][]bool, current Coord) ([][]int, []Coord) {
+	neighbours := [4]Coord{{current.x+1, current.y}, {current.x-1, current.y}, {current.x, current.y+1}, {current.x, current.y-1}}
+	var validNeighbours []Coord
+	for _, neighbour := range neighbours {
+		if neighbour.y < 0 || neighbour.y >= len(grid) || neighbour.x < 0 || neighbour.x >= len(grid[neighbour.y]) {
+			continue
+		}
+
+		if visited[neighbour.y][neighbour.x] {
+			continue
+		}
+
+		validNeighbours = append(validNeighbours, neighbour)
+
+		cost := weights[current.y][current.x] + grid[neighbour.y][neighbour.x]
+
+		if cost < weights[neighbour.y][neighbour.x] {
+			weights[neighbour.y][neighbour.x] = cost
+		}
+	}
+
+	return weights, validNeighbours
+}
+
+func minCost(grid [][]int, src Coord, dest Coord) int {
+	// Create a grid of weights
+	weights := make([][]int, len(grid))
+	for i := range grid {
+		row := make([]int, len(grid[i]))
+		for j := range row {
+			row[j] = 10000000
+		}
+		weights[i] = row
+	}
+
+	visited := make([][]bool, len(grid))
+	for i := range grid {
+		row := make([]bool, len(grid[i]))
+		for j := range row {
+			row[j] = false
+		}
+		visited[i] = row
+	}
+
+	// Set the cost of the src to 0
+	weights[src.y][src.x] = 0
+
+	targets := []Coord{src}
+	iters := 0
+	for !(targets[0].x == dest.x && targets[0].y == dest.y) {
+		var neighbours []Coord
+		weights, neighbours = updateWeights(grid, weights, visited, targets[0])
+		visited[targets[0].y][targets[0].x] = true
+
+		targets = append(targets[1:], neighbours...)
+
+		n := 0
+		for _, t := range targets {
+			if !visited[t.y][t.x] {
+				targets[n] = t
+				n++
+			}
+		}
+		targets = targets[:n]
+
+		sort.Slice(targets, func(i, j int) bool {
+			return weights[targets[i].y][targets[i].x] < weights[targets[j].y][targets[j].x]
+		})
+
+		iters++
+	}
+
+	// printSolution(weights)
+	// fmt.Printf("Took %d iterations\n", iters)
+
+	return weights[dest.y][dest.x]
+}
+
+func main() {
+	challenge := aoc.New(2021, 15)
+
+	challenge.Test(`1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581`, []int{40, 315})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		var grid [][]int
+		for y := 0; input.Scan(); y++ {
+			line := input.Text()
+
+			row := make([]int, len(line))
+
+			for i, c := range line {
+				n, _ := strconv.Atoi(string(c))
+				row[i] = n
+			}
+
+			grid = append(grid, row)
+		}
+
+		// printGrid(grid)
+
+		return minCost(grid, Coord{0, 0}, Coord{len(grid[0])-1, len(grid)-1})
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		var grid [][]int
+		for y := 0; input.Scan(); y++ {
+			line := input.Text()
+
+			row := make([]int, len(line)*5)
+
+			for i, c := range line {
+				n, _ := strconv.Atoi(string(c))
+				for j := 0; j < 5; j++ {
+					v := n + j
+					if v > 9 {
+						v -= 9
+					}
+					row[i+j*len(line)] = v
+				}
+			}
+
+			grid = append(grid, row)
+		}
+
+		height := len(grid)
+		for j := 1; j < 5; j++ {
+			for y := 0; y < height; y++ {
+				row := make([]int, len(grid[y]))
+
+				for x, n := range grid[y] {
+					v := n + j
+					if v > 9 {
+						v -= 9
+					}
+					row[x] = v
+				}
+
+				grid = append(grid, row)
+			}
+		}
+
+		// printGrid(grid)
+
+		return minCost(grid, Coord{0, 0}, Coord{len(grid[0])-1, len(grid)-1})
+	})
+}