From d82e893d09f4fb7417dca83929abde00fcd5f4c6 Mon Sep 17 00:00:00 2001
From: Ivan Lange <langei@mcmaster.ca>
Date: Mon, 29 Jan 2024 01:02:10 -0500
Subject: [PATCH] Add solution that passes test case

---
 sudoku.go        | 17 +++++++++
 sudoku/solver.go | 98 +++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 106 insertions(+), 9 deletions(-)

diff --git a/sudoku.go b/sudoku.go
index 06ab7d0..6a76c9f 100644
--- a/sudoku.go
+++ b/sudoku.go
@@ -1 +1,18 @@
 package main
+
+import "sudoku/sudoku"
+
+// SolveSudoku returns a solved sudoku board
+func SolveSudoku(board [][]int) [][]int {
+
+	const _numWorkers = 100
+
+	solver := sudoku.NewSolver(_numWorkers)
+
+	solution, err := solver.Solve(board)
+	if err != nil {
+		panic(err)
+	}
+
+	return solution
+}
diff --git a/sudoku/solver.go b/sudoku/solver.go
index 178fc6c..c30b3ee 100644
--- a/sudoku/solver.go
+++ b/sudoku/solver.go
@@ -1,20 +1,24 @@
 package sudoku
 
+import "errors"
+
 const (
 	_size        = 9
 	_emptyCell   = 0
 	_maxDigit    = 9
 	_minDigit    = 1
 	_subGridSize = 3
-	_bufSize     = 1000
+	_bufSize     = 100
 )
 
+// boardData is the information required for a goroutine to perform backtracking
 type boardData struct {
 	board [][]int
 	row   int
 	col   int
 }
 
+// Solver contains members for solving a sudoku board
 type Solver struct {
 	numWorkers int
 
@@ -28,21 +32,97 @@ type Solver struct {
 func NewSolver(numWorkers int) *Solver {
 	return &Solver{
 		numWorkers:    numWorkers,
-		boardsToSolve: make(chan boardData),
-		solvedBoard:   make(chan [][]int, _bufSize),
+		boardsToSolve: make(chan boardData, _bufSize),
+		solvedBoard:   make(chan [][]int),
 	}
 }
 
-// Solve returns a solved sudoku board
+// Solve returns a solved sudoku board by spinning up a set number of goroutines which work towards a solution
 func (s *Solver) Solve(board [][]int) ([][]int, error) {
+	if board == nil {
+		return nil, errors.New("board can't be nil")
+	}
+
+	for i := 0; i < s.numWorkers; i++ {
+		go s.parallelSolve()
+	}
+
+	s.boardsToSolve <- boardData{
+		board: board,
+		row:   0,
+		col:   0,
+	}
+
+	solvedBoard := <-s.solvedBoard
 
-	return nil, nil
+	return solvedBoard, nil
+}
+
+// parallelSolve is the work a single goroutine does to work towards the solution
+func (s *Solver) parallelSolve() {
+	var board, newBoard boardData
+
+	for !s.done {
+		board = <-s.boardsToSolve
+
+		if board.row == _size {
+			s.done = true
+			s.solvedBoard <- board.board
+			return
+		}
+
+		if board.col == _size {
+			board.row++
+			board.col = 0
+
+			s.boardsToSolve <- board
+
+			continue
+		}
+
+		if board.board[board.row][board.col] == _emptyCell {
+			for digit := _minDigit; digit <= _maxDigit; digit++ {
+				if s.isValidBoard(board.board, board.row, board.col, digit) {
+					newBoard = boardData{
+						board: copyBoard(board.board),
+						row:   board.row,
+						col:   board.col + 1,
+					}
+
+					newBoard.board[board.row][board.col] = digit
+
+					s.boardsToSolve <- newBoard
+				}
+			}
+		} else {
+			board.col += 1
+			s.boardsToSolve <- board
+		}
+	}
 }
 
 // isValidBoard checks if the board is valid once num is inserted into the specified row and col
 func (s *Solver) isValidBoard(board [][]int, row, col, num int) bool {
-	//for i := 0; i < _size; i++ {
-	//
-	//}
-	return false
+	for i := 0; i < _size; i++ {
+		subGridVal := board[_subGridSize*(row/_subGridSize)+(i/_subGridSize)][_subGridSize*(col/_subGridSize)+i%_subGridSize]
+		colVal := board[row][i]
+		rowVal := board[i][col]
+
+		if subGridVal == num || colVal == num || rowVal == num {
+			return false
+		}
+	}
+	return true
+}
+
+// copyBoard returns a complete copy of a board
+func copyBoard(board [][]int) [][]int {
+	cpy := make([][]int, len(board))
+
+	for i := 0; i < len(board[0]); i++ {
+		cpy[i] = make([]int, len(board[0]))
+		copy(cpy[i], board[i])
+	}
+
+	return cpy
 }