Add code

board.go

@@ -0,0 +1,41 @@
+package main
+
+import "fmt"
+
+const END_OF_GRID cell = 81
+
+type cell uint8
+
+type grid [][]int
+
+func (c cell) row() int {
+	return int(c) / 9
+}
+
+func (c cell) column() int {
+	return int(c) % 9
+}
+
+func (c cell) String() string {
+	return fmt.Sprintf("(%d, %d)", c.row(), c.column())
+}
+
+func (c cell) next() cell {
+	if c >= END_OF_GRID {
+		panic("next() called on cell greater than END_OF_GRID")
+	}
+
+	return c + 1
+}
+
+func (g grid) At(c cell) int {
+	return g[c.row()][c.column()]
+}
+
+func (g grid) Set(c cell, v int) {
+	g[c.row()][c.column()] = v
+}
+
+func (g grid) Reset(c cell) {
+	g[c.row()][c.column()] = 0
+}

sudoku.go

@@ -1 +1,60 @@
 package main
+
+func isMappingValid(g grid, c cell, newValue int) bool {
+	// Check row and column
+	for i := 0; i < 9; i++ {
+		if g[c.row()][i] == newValue || g[i][c.column()] == newValue {
+			return false
+		}
+	}
+
+	// Check box
+	boxRow := c.row() / 3 * 3
+    boxColumn := c.column() / 3 * 3
+    for i := boxRow; i < boxRow + 3; i++ {
+        for j := boxColumn; j < boxColumn + 3; j++ {
+			if i == c.row() || j == c.column() { // row and column already checked, so skip
+				continue
+			}
+
+            if g[i][j] == newValue {
+                return false
+            }
+        }
+    }
+
+	return true
+}
+
+func SolveSudokuRecursive(inputGrid grid, c cell) (solvedGrid [][]int) {
+	if c == END_OF_GRID {
+		return Copy(inputGrid)
+	}
+
+	if inputGrid.At(c) != 0 {
+		return SolveSudokuRecursive(inputGrid, c.next())
+	}
+
+	for i := 1; i <= 9; i++ {
+		if !isMappingValid(inputGrid, c, i) {
+			continue
+		}
+
+		inputGrid.Set(c, i)
+		solveChild := SolveSudokuRecursive(inputGrid, c.next())
+		inputGrid.Reset(c)
+
+		if solveChild != nil {
+			return solveChild
+		}
+	}
+
+	return nil
+}
+
+func SolveSudoku(inputGrid grid) (solvedGrid [][]int) {
+	return SolveSudokuRecursive(inputGrid, 0)
+}
+
+func main() {
+}

utils.go

@@ -0,0 +1,15 @@
+package main
+
+func Copy[T any](s [][]T) [][]T {
+	copy := make([][]T, len(s))
+
+	for i := 0; i < len(s); i++ {
+		copy[i] = make([]T, len(s[i]))
+
+		for j, v := range s[i] {
+			copy[i][j] = v
+		}
+	}
+
+	return copy
+}