feat: day 04 part 2 solution

Author: agrmohit

2024/04/main.go

@@ -33,8 +33,49 @@ func solvePart1(input string) int {
 	return len(words)
 }
 
+func solvePart2(input string) int {
+	characterGrid, err := inputs.ExtractCharacterGrid(input)
+	if err != nil {
+		log.Fatalf("ERROR: %v", err)
+	}
+
+	// Thats wayyy too many nested slices but it workd :-)
+	subgrids := [][][]byte{}
+	subgridCount := 0
+
+	subgrids = append(subgrids, [][]byte{
+		{'M', '.', 'M'},
+		{'.', 'A', '.'},
+		{'S', '.', 'S'},
+	})
+	subgrids = append(subgrids, [][]byte{
+		{'M', '.', 'S'},
+		{'.', 'A', '.'},
+		{'M', '.', 'S'},
+	})
+	subgrids = append(subgrids, [][]byte{
+		{'S', '.', 'M'},
+		{'.', 'A', '.'},
+		{'S', '.', 'M'},
+	})
+	subgrids = append(subgrids, [][]byte{
+		{'S', '.', 'S'},
+		{'.', 'A', '.'},
+		{'M', '.', 'M'},
+	})
+
+	for _, subgrid := range subgrids {
+		subgridLocationList := grid.FindSubgridsInGrid(characterGrid, subgrid, '.')
+		subgridCount += len(subgridLocationList)
+	}
+
+	return subgridCount
+}
+
 func main() {
 	part1Solution := solvePart1(input)
+	part2Solution := solvePart2(input)
 
 	fmt.Println("Day 04 Part 1 solution:", part1Solution)
+	fmt.Println("Day 04 Part 2 solution:", part2Solution)
 }

2024/04/main_test.go

@@ -11,6 +11,12 @@ var test1 string
 //go:embed test2.txt
 var test2 string
 
+//go:embed test3.txt
+var test3 string
+
+//go:embed test4.txt
+var test4 string
+
 func TestSolution(t *testing.T) {
 	t.Run("Day 04 part 1 test 1", func(t *testing.T) {
 		want := 4
@@ -29,4 +35,22 @@ func TestSolution(t *testing.T) {
 			t.Errorf("Incorrect solution, got %d want %d", got, want)
 		}
 	})
+
+	t.Run("Day 04 part 2 test 1", func(t *testing.T) {
+		want := 1
+		got := solvePart2(test3)
+
+		if got != want {
+			t.Errorf("Incorrect solution, got %d want %d", got, want)
+		}
+	})
+
+	t.Run("Day 04 part 2 test 2", func(t *testing.T) {
+		want := 9
+		got := solvePart2(test4)
+
+		if got != want {
+			t.Errorf("Incorrect solution, got %d want %d", got, want)
+		}
+	})
 }

2024/04/test3.txt

@@ -0,0 +1,3 @@
+M.S
+.A.
+M.S

2024/04/test4.txt

@@ -0,0 +1,10 @@
+.M.S......
+..A..MSMS.
+.M.S.MAA..
+..A.ASMSM.
+.M.S.M....
+..........
+S.S.S.S.S.
+.A.A.A.A..
+M.M.M.M.M.
+..........

internal/grid/subgrid.go

@@ -0,0 +1,54 @@
+package grid
+
+// SubgridLocation represents the coordinates of a found subgrid in the grid
+type SubgridLocation struct {
+	Subgrid [][]byte // Subgrid is the subgrid that was found in the grid
+	StartX  int      // StartX is the starting x-coordinate of the subgrid in the grid
+	StartY  int      // StartY is the starting y-coordinate of the subgrid in the grid
+	EndX    int      // EndX is the ending x-coordinate of the subgrid in the grid
+	EndY    int      // EndY is the ending y-coordinate of the subgrid in the grid
+}
+
+// FindSubgridsInGrid searches for subgrids in a given grid
+//
+// '.' could be any character in the grid. All other characters need an exact match.
+// wildcardCharacter in subgrid can match any character in grid
+func FindSubgridsInGrid(grid, subgrid [][]byte, wildcardCharacter byte) []SubgridLocation {
+	var result []SubgridLocation
+
+	for i, row := range grid {
+		for j := range row {
+			sgl := checkIndexForSubgrid(i, j, grid, subgrid, wildcardCharacter)
+			if len(sgl.Subgrid) != 0 {
+				result = append(result, sgl)
+			}
+		}
+	}
+	return result
+}
+
+func checkIndexForSubgrid(i, j int, grid, subgrid [][]byte, wildcardCharacter byte) SubgridLocation {
+	var result SubgridLocation
+
+	for si, row := range subgrid {
+		for sj := range row {
+			// Check whether subgrid exceeds the bounds of grid
+			if i+len(subgrid) > len(grid) || j+len(subgrid[0]) > len(grid[0]) {
+				return result
+			}
+
+			// Check whether the character matches or is the wildcard character
+			if !(subgrid[si][sj] == wildcardCharacter || subgrid[si][sj] == grid[i+si][j+sj]) {
+				return result
+			}
+		}
+	}
+
+	result.Subgrid = subgrid
+	result.StartX = j
+	result.StartY = i
+	result.EndX = j + len(subgrid[0]) - 1
+	result.EndY = i + len(subgrid) - 1
+
+	return result
+}