Solution for 11.1

2018/day11-1.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"fmt"
+
+	"internal/day11"
+	"internal/util"
+)
+
+func main() {
+	serialNumber := util.ReadInputInts()[0]
+
+	grid := day11.GenerateGrid(serialNumber)
+	x, y := day11.FindBestWindow3x3(grid)
+
+	fmt.Printf("%d,%d\n", x, y)
+}

2018/internal/day11/debug.go

@@ -0,0 +1,23 @@
+package day11
+
+import (
+	"fmt"
+)
+
+func DebugPrintGrid(grid [][]int) {
+	for y := 0; y < GridSize; y++ {
+		for x := 0; x < GridSize; x++ {
+			fmt.Printf("%3d", grid[y][x])
+		}
+		fmt.Println()
+	}
+}
+
+func DebugPrint5x5(grid [][]int, x, y int) {
+	for i := y - 1; i < y+4; i++ {
+		for j := x - 1; j < x+4; j++ {
+			fmt.Printf("%3d", grid[i][j])
+		}
+		fmt.Println()
+	}
+}

2018/internal/day11/power.go

@@ -0,0 +1,64 @@
+package day11
+
+const GridSize = 300
+
+func GenerateGrid(serialNumber int) [][]int {
+	grid := make([][]int, GridSize)
+	for i := 0; i < GridSize; i++ {
+		grid[i] = make([]int, GridSize)
+	}
+
+	// Calculate the power level in each fuel cell
+	for y := 0; y < GridSize; y++ {
+		for x := 0; x < GridSize; x++ {
+			// Find the fuel cell's rack ID, which is its X coordinate plus 10.
+			rackID := (x + 1) + 10
+			// Begin with a power level of the rack ID times the Y coordinate.
+			// Increase the power level by the value of the grid serial number (your puzzle input).
+			// Set the power level to itself multiplied by the rack ID.
+			power := ((rackID * (y + 1)) + serialNumber) * rackID
+
+			// Keep only the hundreds digit of the power level (so 12345 becomes 3; numbers with no hundreds digit become 0).
+			power = (power % 1000) / 100
+
+			// Subtract 5 from the power level.
+			power -= 5
+
+			grid[y][x] = power
+		}
+	}
+
+	return grid
+}
+
+func FindBestWindow3x3(grid [][]int) (int, int) {
+	largest := sumNxN(grid, 0, 0, 3)
+	bestX := 0
+	bestY := 0
+
+	for x := 1; x < GridSize-2; x++ {
+		for y := 1; y < GridSize-2; y++ {
+			sum := sumNxN(grid, x, y, 3)
+
+			if sum > largest {
+				largest = sum
+				bestX = x
+				bestY = y
+			}
+		}
+	}
+
+	return bestX + 1, bestY + 1
+}
+
+func sumNxN(grid [][]int, x, y, n int) int {
+	total := 0
+
+	for i := 0; i < n; i++ {
+		for j := 0; j < n; j++ {
+			total += grid[y+i][x+j]
+		}
+	}
+
+	return total
+}