From b20b1c44b3f43ab1e53312d01d8d9bc7bb267615 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Fri, 25 Dec 2020 15:16:37 -0500
Subject: [PATCH] 2016-day24: bfs to make weighted graph -> dfs to find
 shortest path through all nodes

---
 2016/day24/main.go      | 137 ++++++++++++++++++++++++++++++++++++++++
 2016/day24/main_test.go |  33 ++++++++++
 2 files changed, 170 insertions(+)
 create mode 100644 2016/day24/main.go
 create mode 100644 2016/day24/main_test.go

diff --git a/2016/day24/main.go b/2016/day24/main.go
new file mode 100644
index 0000000..64483cf
--- /dev/null
+++ b/2016/day24/main.go
@@ -0,0 +1,137 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/mathutil"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := cleaningRobot(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func cleaningRobot(input string, part int) int {
+	var grid [][]string
+	for _, l := range strings.Split(input, "\n") {
+		grid = append(grid, strings.Split(l, ""))
+	}
+
+	// bfs from every numbered cell to every other
+	// generate a weighted graph
+	var graph [][]int
+	for r, row := range grid {
+		for c, cell := range row {
+			if regexp.MustCompile("[0-9]").MatchString(cell) {
+				poi := cell
+				distancesFromPOI := bfsGetEdgeWeights(grid, [2]int{r, c})
+				// initialize graph size
+				if graph == nil {
+					for i := 0; i < len(distancesFromPOI); i++ {
+						graph = append(graph, make([]int, len(distancesFromPOI)))
+					}
+				}
+				graph[cast.ToInt(poi)] = distancesFromPOI
+			}
+		}
+	}
+
+	// then a recursive, backtracking dfs on that weighted graph to determine
+	// the shortest total path
+	returnToZero := part != 1
+	return dfs(graph, 0, map[int]bool{0: true}, returnToZero)
+}
+
+type bfsNode struct {
+	row, col int // 0,0 is top left
+	distance int
+}
+
+// allows passing through points of interest
+func bfsGetEdgeWeights(grid [][]string, start [2]int) []int {
+	// points of interest to distance to reach them from the starting coord
+	poiToDistance := map[string]int{
+		grid[start[0]][start[1]]: 0,
+	}
+	// run until all nodes have been seen...
+	queue := []bfsNode{
+		{start[0], start[1], 0},
+	}
+	visited := map[[2]int]bool{}
+	for len(queue) > 0 {
+		front := queue[0]
+		queue = queue[1:]
+
+		if visited[[2]int{front.row, front.col}] {
+			continue
+		}
+		visited[[2]int{front.row, front.col}] = true
+
+		if regexp.MustCompile("[0-9]").MatchString(grid[front.row][front.col]) {
+			poiToDistance[grid[front.row][front.col]] = front.distance
+		}
+		for _, d := range dirs {
+			nextRow, nextCol := front.row+d[0], front.col+d[1]
+			// don't need to check for going out of bounds because there are walls
+			// surrounding everything
+			if grid[nextRow][nextCol] != "#" {
+				queue = append(queue, bfsNode{
+					row:      nextRow,
+					col:      nextCol,
+					distance: front.distance + 1,
+				})
+			}
+		}
+
+	}
+
+	distances := make([]int, len(poiToDistance))
+	for numStr, dist := range poiToDistance {
+		distances[cast.ToInt(numStr)] = dist
+	}
+	return distances
+}
+
+var dirs = [][2]int{
+	{0, -1},
+	{0, 1},
+	{1, 0},
+	{-1, 0},
+}
+
+func dfs(graph [][]int, entryIndex int, visited map[int]bool, returnToZero bool) (minWeightSum int) {
+	// if all nodes have been visited, return zero for part 1, or the distance
+	// from the entryIndex to the zero POI
+	if len(graph) == len(visited) {
+		if returnToZero {
+			return graph[entryIndex][0]
+		}
+		return 0
+	}
+
+	// get the minimum distance from a recursive call
+	minDistance := math.MaxInt32
+	for i, val := range graph[entryIndex] {
+		if !visited[i] {
+			visited[i] = true
+
+			dist := val + dfs(graph, i, visited, returnToZero)
+			minDistance = mathutil.MinInt(minDistance, dist)
+
+			delete(visited, i)
+		}
+	}
+
+	return minDistance
+}
diff --git a/2016/day24/main_test.go b/2016/day24/main_test.go
new file mode 100644
index 0000000..8d15030
--- /dev/null
+++ b/2016/day24/main_test.go
@@ -0,0 +1,33 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var example = `###########
+#0.1.....2#
+#.#######.#
+#4.......3#
+###########`
+
+func Test_cleaningRobot(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"part1 example", example, 1, 14},
+		{"part1 actual", util.ReadFile("input.txt"), 1, 442},
+		{"part2 actual", util.ReadFile("input.txt"), 2, 660},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := cleaningRobot(tt.input, tt.part); got != tt.want {
+				t.Errorf("cleaningRobot() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}