Add func IsIn2DArray(c, m) bool

Complete method signature:
```go
func In2DArray[T any](
  c util.Coordinate,
  m [][]T,
) bool
```

Author: terminalnode

common/util/coordinate.go

@@ -7,6 +7,16 @@ type Coordinate struct {
 
 type Direction = func(c Coordinate) Coordinate
 
+func In2DArray[T any](
+	c Coordinate,
+	m [][]T,
+) bool {
+	invalid := len(m) == 0 || len(m[0]) == 0 ||
+		c.X < 0 || c.X >= len(m[0]) ||
+		c.Y < 0 || c.Y >= len(m)
+	return !invalid
+}
+
 func (c Coordinate) North() Coordinate {
 	return Coordinate{c.X, c.Y - 1}
 }

common/util/coordinate_test.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"fmt"
 	"testing"
 )
 
@@ -28,3 +29,45 @@ func TestCoordinateDirections(t *testing.T) {
 		})
 	}
 }
+
+func TestIn2DArray(t *testing.T) {
+	matrix := [][]int{{0, 0}, {0, 0}}
+	tests := []struct {
+		c        Coordinate
+		expected bool
+	}{
+		// Top left corner
+		{Coordinate{X: -1, Y: -1}, false},
+		{Coordinate{X: +0, Y: -1}, false},
+		{Coordinate{X: -1, Y: +0}, false},
+		{Coordinate{X: +0, Y: +0}, true},
+
+		// Top right corner
+		{Coordinate{X: +1, Y: -1}, false},
+		{Coordinate{X: +2, Y: -1}, false},
+		{Coordinate{X: +1, Y: +0}, true},
+		{Coordinate{X: +2, Y: +0}, false},
+
+		// Bottom left corner
+		{Coordinate{X: -1, Y: +1}, false},
+		{Coordinate{X: +0, Y: +1}, true},
+		{Coordinate{X: -1, Y: +2}, false},
+		{Coordinate{X: +0, Y: +2}, false},
+
+		// Bottom right corner
+		{Coordinate{X: +1, Y: +1}, true},
+		{Coordinate{X: +2, Y: +1}, false},
+		{Coordinate{X: +1, Y: +2}, false},
+		{Coordinate{X: +2, Y: +2}, false},
+	}
+
+	for _, test := range tests {
+		name := fmt.Sprintf("%v in 2D matrix", test.c)
+		t.Run(name, func(t *testing.T) {
+			actual := In2DArray(test.c, matrix)
+			if test.expected != actual {
+				t.Errorf("expected In2DArray(test.c, matrix) == %v but got %v", test.expected, actual)
+			}
+		})
+	}
+}