Solution

sudoku.go

@@ -1 +1,61 @@
 package main
+
+//Returns a set of all possible solutions for the specified position
+func GetSolns(input [][]int, pos_x int, pos_y int) map[int]bool {
+	var possible_solns map[int]bool = map[int]bool{1: true, 2: true, 3: true, 4: true, 5: true, 6: true, 7: true, 8: true, 9: true} // I wish there was a proper Set type
+
+	// Remove numbers in same row and column from possible solutions
+	for i := 0; i < 9; i++ {
+		delete(possible_solns, input[pos_y][i])
+		delete(possible_solns, input[i][pos_x])
+	}
+
+	box_x := (pos_x / 3) * 3
+	box_y := (pos_y / 3) * 3 // Rounds to the upper left corner of 3x3 box
+
+	// Remove numbers in same box from possible solutions
+	for dx := 0; dx < 3; dx++ {
+		for dy := 0; dy < 3; dy++ {
+			delete(possible_solns, input[box_y+dy][box_x+dx])
+		}
+	}
+
+	return possible_solns
+}
+
+// Solves the puzzle (if solvable) starting from the given location and
+// returns true. Otherwise, returns false and the puzzle is unmodified.
+func RunSolve(input [][]int, pos_x int, pox_y int) bool {
+
+	//move x, y to the first blank
+	for input[pox_y][pos_x] != 0 {
+		pos_x++
+		if pos_x == 9 {
+			pos_x = 0
+			pox_y++
+			if pox_y == 9 {
+				return true // Base case 1: there are no more blank values to solve for
+			}
+		}
+	}
+
+	possible_solns := GetSolns(input, pos_x, pox_y)
+
+	// Reccursive step: try every solution generated. If one solves it, good. If not, continue.
+	// Because the reccursive step reduceses the blank areas by one, the reccursive call must
+	// return at some point because of base case #1.
+	for soln := range possible_solns {
+		input[pox_y][pos_x] = soln
+		if RunSolve(input, pos_x, pox_y) {
+			return true 
+		}
+	}
+
+	input[pox_y][pos_x] = 0
+	return false // Base case 2: Either the input puzzle has no solution (len(possible_solns) == 0) or all the possible solns failed.
+}
+
+func SolveSudoku(input [][]int) [][]int {
+	RunSolve(input, 0, 0)
+	return input
+}