Day 11.2 solution.

2018/day11-2.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, n := day11.FindBestWindow(grid)
+
+	fmt.Printf("%d,%d,%d\n", x, y, n)
+}

2018/internal/day11/debug.go

@@ -13,9 +13,9 @@ func DebugPrintGrid(grid [][]int) {
 	}
 }
 
-func DebugPrint5x5(grid [][]int, x, y int) {
+func DebugPrintNxN(grid [][]int, x, y, n int) {
-	for i := y - 1; i < y+4; i++ {
+	for i := y; i < y+n; i++ {
-		for j := x - 1; j < x+4; j++ {
+		for j := x; j < x+n; j++ {
 			fmt.Printf("%3d", grid[i][j])
 		}
 		fmt.Println()

2018/internal/day11/power.go

@@ -1,5 +1,9 @@
 package day11
 
+import (
+	"internal/util"
+)
+
 const GridSize = 300
 
 func GenerateGrid(serialNumber int) [][]int {
@@ -62,3 +66,48 @@ func sumNxN(grid [][]int, x, y, n int) int {
 
 	return total
 }
+
+func FindBestWindow(grid [][]int) (int, int, int) {
+	largest := grid[0][0]
+	bestX := 0
+	bestY := 0
+	bestN := 1
+
+	for x := 0; x < GridSize; x++ {
+		for y := 0; y < GridSize; y++ {
+			sum, n := findBestSquare(grid, x, y)
+
+			if sum > largest {
+				largest = sum
+				bestX = x
+				bestY = y
+				bestN = n
+			}
+		}
+	}
+
+	return bestX + 1, bestY + 1, bestN
+}
+
+func findBestSquare(grid [][]int, x, y int) (int, int) {
+	sum := grid[y][x]
+	bestSum := sum
+	bestN := 1
+
+	for n := 2; n < util.Min(GridSize-y, GridSize-x); n++ {
+		for i := y; i < y+n; i++ {
+			sum += grid[i][x+n-1]
+		}
+
+		for i := x; i < x+n-1; i++ {
+			sum += grid[y+n-1][i]
+		}
+
+		if sum > bestSum {
+			bestSum = sum
+			bestN = n
+		}
+	}
+
+	return bestSum, bestN
+}

2018/internal/util/math.go

@@ -1,8 +1,15 @@
 package util
 
-func abs(x int) int {
+func Abs(x int) int {
 	if x < 0 {
 		return -x
 	}
 	return x
 }
+
+func Min(i, j int) int {
+	if i < j {
+		return i
+	}
+	return j
+}