2017-day19: simple following a 2D path

2017/day19/main.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"regexp"
+	"strings"
+
+	"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)
+
+	visitedChars, steps := movePacket(util.ReadFile("./input.txt"))
+	if part == 1 {
+		fmt.Println("Output:", visitedChars)
+	} else {
+		fmt.Println("Output:", steps)
+	}
+}
+
+var dirs = [4][2]int{
+	{1, 0},  // down
+	{0, -1}, // left
+	{-1, 0}, // up
+	{0, 1},  // right
+}
+
+var pathRegexp = regexp.MustCompile("^[-|+A-Z]$")
+var capsRegexp = regexp.MustCompile("^[A-Z]$")
+
+func movePacket(input string) (visitedChars string, steps int) {
+	grid := parseInput(input)
+	// finding starting point in first row
+	var row, col int
+	for c := 0; c < len(grid[0]); c++ {
+		if grid[0][c] == "|" {
+			col = c
+			break
+		}
+	}
+
+	// track which index in dirs is the current directions, start facing down
+	var dirIndex int
+
+	// include starting tile...
+	steps = 1
+
+	// basically an infinite loop...
+	for i := 0; i < math.MaxInt64; i++ {
+		inFrontVal := getNextValue(grid, row, col, dirs[dirIndex])
+
+		if pathRegexp.MatchString(inFrontVal) {
+			row += dirs[dirIndex][0]
+			col += dirs[dirIndex][1]
+			steps++
+
+			// also check if it's a letter
+			if capsRegexp.MatchString(inFrontVal) {
+				visitedChars += inFrontVal
+			}
+		} else if inFrontVal == " " {
+			// just try to turn right then left, assuming no 3 way intersections...
+			dirIndex = (dirIndex + 1) % 4
+			if pathRegexp.MatchString(getNextValue(grid, row, col, dirs[dirIndex])) {
+				continue
+			}
+
+			// if right isn't a path, then try to turn left from original direction
+			// i.e. add 2 more & mod
+			dirIndex = (dirIndex + 2) % 4
+			if pathRegexp.MatchString(getNextValue(grid, row, col, dirs[dirIndex])) {
+				continue
+			}
+
+			// can't turn, break out of loop
+			break
+		} else {
+			panic("unhandled char " + inFrontVal)
+		}
+	}
+
+	return visitedChars, steps
+}
+
+func getNextValue(grid [][]string, row, col int, diff [2]int) string {
+	inFrontRow := row + diff[0]
+	inFrontCol := col + diff[1]
+	// if not in bounds, just return a space
+	if inFrontRow < 0 || inFrontRow >= len(grid) || inFrontCol < 0 || inFrontCol >= len(grid[0]) {
+		return " "
+	}
+	return grid[inFrontRow][inFrontCol]
+}
+
+func parseInput(input string) [][]string {
+	var grid [][]string
+
+	for _, line := range strings.Split(input, "\n") {
+		grid = append(grid, strings.Split(line, ""))
+	}
+	return grid
+}

2017/day19/main_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+// easier to look at this input in the format, but need to remove leading/trailing newlines
+var example = strings.Trim(`
+    |         
+    |  +--+   
+    A  |  C   
+F---|----E|--+
+    |  |  |  D
+    +B-+  +--+
+`, "\n")
+
+func Test_movePacket(t *testing.T) {
+	tests := []struct {
+		name             string
+		input            string
+		wantVisitedChars string
+		wantSteps        int
+	}{
+		{"example", example, "ABCDEF", 38},
+		{"actual", util.ReadFile("input.txt"), "EPYDUXANIT", 17544},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotVisitedChars, gotSteps := movePacket(tt.input)
+			if gotVisitedChars != tt.wantVisitedChars {
+				t.Errorf("movePacket() gotVisitedChars = %v, want %v", gotVisitedChars, tt.wantVisitedChars)
+			}
+			if gotSteps != tt.wantSteps {
+				t.Errorf("movePacket() gotSteps = %v, want %v", gotSteps, tt.wantSteps)
+			}
+		})
+	}
+}