dsasse07/sudoku-full.js

## sudoku-full.js
const BLANK_BOARD = [
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0]
]

let counter
const numArray = [1, 2, 3, 4, 5, 6, 7, 8, 9]

function shuffle( array ) {
  let newArray = [...array]
  for ( let i = newArray.length - 1; i > 0; i-- ) {
      const j = Math.floor( Math.random() * ( i + 1 ) );
      [ newArray[ i ], newArray[ j ] ] = [ newArray[ j ], newArray[ i ] ];
  }
  return newArray;
}


/*--------------------------------------------------------------------------------------------
--------------------------------- Check if Location Safe -------------------------------------
--------------------------------------------------------------------------------------------*/

const rowSafe = (puzzleArray, emptyCell, num) => {
  // -1 is return value of .find() if value not found
  return puzzleArray[ emptyCell.rowIndex ].indexOf(num) == -1
}
const colSafe = (puzzleArray, emptyCell, num) => {
  return !puzzleArray.some(row => row[ emptyCell.colIndex ] == num )
}

const boxSafe = (puzzleArray, emptyCell, num) => {
  boxStartRow = emptyCell.rowIndex - (emptyCell.rowIndex % 3) // Define top left corner of box region for empty cell
  boxStartCol = emptyCell.colIndex - (emptyCell.colIndex % 3)
  let safe = true

  for ( boxRow of [0,1,2] ) {  // Each box region has 3 rows
    for ( boxCol of [0,1,2] ) { // Each box region has 3 columns
      if ( puzzleArray[boxStartRow + boxRow][boxStartCol + boxCol] == num ) { // Num is present in box region?
        safe = false // If number is found, it is not safe to place
      }
    }
  }
  return safe
}

const safeToPlace = ( puzzleArray, emptyCell, num ) => {
  return rowSafe(puzzleArray, emptyCell, num) &&
  colSafe(puzzleArray, emptyCell, num) &&
  boxSafe(puzzleArray, emptyCell, num)
}

/*--------------------------------------------------------------------------------------------
--------------------------------- Obtain Next Empty Cell -------------------------------------
--------------------------------------------------------------------------------------------*/

const nextEmptyCell = puzzleArray => {
  const emptyCell = {rowIndex: "", colIndex: ""}

  puzzleArray.forEach( (row, rowIndex) => {
      if (emptyCell.colIndex !== "" ) return // If this key has already been assigned, skip iteration
      let firstZero = row.find( col => col === 0) // find first zero-element
      if (firstZero === undefined) return; // if no zero present, skip to next row
      emptyCell.rowIndex = rowIndex
      emptyCell.colIndex = row.indexOf(firstZero)
    })

  if (emptyCell.colIndex !== "" ) return emptyCell
  // If emptyCell was never assigned, there are no more zeros
  return false
}

/*--------------------------------------------------------------------------------------------
--------------------------------- Generate Filled Board -------------------------------------
--------------------------------------------------------------------------------------------*/

const fillPuzzle = startingBoard => {
  const emptyCell = nextEmptyCell(startingBoard)
  // If there are no more zeros, the board is finished, return it
  if (!emptyCell) return startingBoard

  // Shuffled [0 - 9 ] array fills board randomly each pass
  for (num of shuffle(numArray) ) {
    // counter is a global variable tracking the number of iterations performed in generating a puzzle
    // Most puzzles generate in < 500ms, but occassionally random generation could run in to
    // heavy backtracking and result in a long wait. Best to abort this attempt and restart.
    // 20_000_000 iteration maximum is approximately 1.3 sec runtime.
    // See initializer function for more
    counter++
    if ( counter > 20_000_000 ) throw new Error ("Recursion Timeout")
    if ( safeToPlace( startingBoard, emptyCell, num) ) {
      startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = num // If safe to place number, place it
      // Recursively call the fill function to place num in next empty cell
      if ( fillPuzzle(startingBoard) ) return startingBoard
      // If we were unable to place the future num, that num was wrong. Reset it and try next value
      startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = 0
    }
  }
  return false // If unable to place any number, return false, which triggers previous round to go to next num
}

const newSolvedBoard = _ => {
  const newBoard = BLANK_BOARD.map(row => row.slice() ) // Create an unaffiliated clone of a fresh board
  fillPuzzle(newBoard) // Populate the board using backtracking algorithm
  return newBoard
}

/*--------------------------------------------------------------------------------------------
--------------------------------- Generate Playable Board ------------------------------------
--------------------------------------------------------------------------------------------*/

const pokeHoles = (startingBoard, holes) => {
  const removedVals = []

  while (removedVals.length < holes) {
    const val = Math.floor(Math.random() * 81) // Value between 0-81
    const randomRowIndex = Math.floor(val / 9) // Integer 0-8 for row index
    const randomColIndex = val % 9

    if (!startingBoard[ randomRowIndex ]) continue // guard against cloning error
    if ( startingBoard[ randomRowIndex ][ randomColIndex ] == 0 ) continue // If cell already empty, restart loop

    removedVals.push({  // Store the current value at the coordinates
      rowIndex: randomRowIndex,
      colIndex: randomColIndex,
      val: startingBoard[ randomRowIndex ][ randomColIndex ]
    })
    startingBoard[ randomRowIndex ][ randomColIndex ] = 0 // "poke a hole" in the board at the coords
    const proposedBoard = startingBoard.map ( row => row.slice() ) // Clone this changed board

    // Attempt to solve the board after removing value. If it cannot be solved, restore the old value.
    // and remove that option from the list
    if ( !fillPuzzle( proposedBoard ) ) {
      startingBoard[ randomRowIndex ][ randomColIndex ] = removedVals.pop().val
    }
  }
  return [removedVals, startingBoard]
}

/*--------------------------------------------------------------------------------------------
--------------------------------- Initialize -------------------------------------
--------------------------------------------------------------------------------------------*/

function newStartingBoard  (holes) {
  // Reset global iteration counter to 0 and Try to generate a new game.
  // If counter reaches its maximum limit in the fillPuzzle function, current attemp will abort
  // To prevent the abort from crashing the script, the error is caught and used to re-run
  // this function
  try {
    counter = 0
    let solvedBoard = newSolvedBoard()

    // Clone the populated board and poke holes in it.
    // Stored the removed values for clues
    let [removedVals, startingBoard] = pokeHoles( solvedBoard.map ( row => row.slice() ), holes)

    return [removedVals, startingBoard, solvedBoard]

  } catch (error)
    return newStartingBoard(holes)
  }
}

// The board will be completely solved once for each item in the empty cell list.
// The empty cell array is rotated on each iteration, so that the order of the empty cells
// And thus the order of solving the game, is different each time.
// The solution for each attempt is pushed to a possibleSolutions array as a string
// Multiple solutions are identified by taking a unique Set from the possible solutions
// and measuring its length. If multiple possible solutions are found at any point
// If will return true, prompting the pokeHoles function to select a new value for removal.

function multiplePossibleSolutions (boardToCheck) {
  const possibleSolutions = []
  const emptyCellArray = emptyCellCoords(boardToCheck)
  for (let index = 0; index < emptyCellArray.length; index++) {
    // Rotate a clone of the emptyCellArray by one for each iteration
    emptyCellClone = [...emptyCellArray]
    const startingPoint = emptyCellClone.splice(index, 1);
    emptyCellClone.unshift( startingPoint[0] )
    thisSolution = fillFromArray( boardToCheck.map( row => row.slice() ) , emptyCellClone)
    possibleSolutions.push( thisSolution.join() )
    if (Array.from(new Set(possibleSolutions)).length > 1 ) return true
  }
  return false
}

// This will attempt to solve the puzzle by placing values into the board in the order that
// the empty cells list presents
function fillFromArray(startingBoard, emptyCellArray) {
  const emptyCell = nextStillEmptyCell(startingBoard, emptyCellArray)
  if (!emptyCell) return startingBoard
  for (num of shuffle(numArray) ) {
    pokeCounter++
    if ( pokeCounter > 60_000_000 ) throw new Error ("Poke Timeout")
    if ( safeToPlace( startingBoard, emptyCell, num) ) {
      startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = num
      if ( fillFromArray(startingBoard, emptyCellArray) ) return startingBoard
      startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = 0
    }
  }
  return false
}

// As numbers get placed, not all of the initial cells are still empty.
// This will find the next still empty cell in the list
function nextStillEmptyCell (startingBoard, emptyCellArray) {
  for (coords of emptyCellArray) {
    if (startingBoard[ coords.row ][ coords.col ] === 0) return {rowIndex: coords.row, colIndex: coords.col}
  }
  return false
}

// Generate array from range, inclusive of start & endbounds.
const range = (start, end) => {
  const length = end - start + 1
  return Array.from( {length} , ( _ , i) => start + i)
}

// Get a list of all empty cells in the board from top-left to bottom-right
function emptyCellCoords (startingBoard) {
  const listOfEmptyCells = []
  for (const row of range(0,8)) {
    for (const col of range(0,8) ) {
      if (startingBoard[row][col] === 0 ) listOfEmptyCells.push( {row, col } )
    }
  }
  return listOfEmptyCells
}
	const BLANK_BOARD = [
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0],
	[0, 0, 0, 0, 0, 0, 0, 0, 0]
	]

	let counter
	const numArray = [1, 2, 3, 4, 5, 6, 7, 8, 9]

	function shuffle( array ) {
	let newArray = [...array]
	for ( let i = newArray.length - 1; i > 0; i-- ) {
	const j = Math.floor( Math.random() * ( i + 1 ) );
	[ newArray[ i ], newArray[ j ] ] = [ newArray[ j ], newArray[ i ] ];
	}
	return newArray;
	}


	/*--------------------------------------------------------------------------------------------
	--------------------------------- Check if Location Safe -------------------------------------
	--------------------------------------------------------------------------------------------*/

	const rowSafe = (puzzleArray, emptyCell, num) => {
	// -1 is return value of .find() if value not found
	return puzzleArray[ emptyCell.rowIndex ].indexOf(num) == -1
	}
	const colSafe = (puzzleArray, emptyCell, num) => {
	return !puzzleArray.some(row => row[ emptyCell.colIndex ] == num )
	}

	const boxSafe = (puzzleArray, emptyCell, num) => {
	boxStartRow = emptyCell.rowIndex - (emptyCell.rowIndex % 3) // Define top left corner of box region for empty cell
	boxStartCol = emptyCell.colIndex - (emptyCell.colIndex % 3)
	let safe = true

	for ( boxRow of [0,1,2] ) { // Each box region has 3 rows
	for ( boxCol of [0,1,2] ) { // Each box region has 3 columns
	if ( puzzleArray[boxStartRow + boxRow][boxStartCol + boxCol] == num ) { // Num is present in box region?
	safe = false // If number is found, it is not safe to place
	}
	}
	}
	return safe
	}

	const safeToPlace = ( puzzleArray, emptyCell, num ) => {
	return rowSafe(puzzleArray, emptyCell, num) &&
	colSafe(puzzleArray, emptyCell, num) &&
	boxSafe(puzzleArray, emptyCell, num)
	}

	/*--------------------------------------------------------------------------------------------
	--------------------------------- Obtain Next Empty Cell -------------------------------------
	--------------------------------------------------------------------------------------------*/

	const nextEmptyCell = puzzleArray => {
	const emptyCell = {rowIndex: "", colIndex: ""}

	puzzleArray.forEach( (row, rowIndex) => {
	if (emptyCell.colIndex !== "" ) return // If this key has already been assigned, skip iteration
	let firstZero = row.find( col => col === 0) // find first zero-element
	if (firstZero === undefined) return; // if no zero present, skip to next row
	emptyCell.rowIndex = rowIndex
	emptyCell.colIndex = row.indexOf(firstZero)
	})

	if (emptyCell.colIndex !== "" ) return emptyCell
	// If emptyCell was never assigned, there are no more zeros
	return false
	}

	/*--------------------------------------------------------------------------------------------
	--------------------------------- Generate Filled Board -------------------------------------
	--------------------------------------------------------------------------------------------*/

	const fillPuzzle = startingBoard => {
	const emptyCell = nextEmptyCell(startingBoard)
	// If there are no more zeros, the board is finished, return it
	if (!emptyCell) return startingBoard

	// Shuffled [0 - 9 ] array fills board randomly each pass
	for (num of shuffle(numArray) ) {
	// counter is a global variable tracking the number of iterations performed in generating a puzzle
	// Most puzzles generate in < 500ms, but occassionally random generation could run in to
	// heavy backtracking and result in a long wait. Best to abort this attempt and restart.
	// 20_000_000 iteration maximum is approximately 1.3 sec runtime.
	// See initializer function for more
	counter++
	if ( counter > 20_000_000 ) throw new Error ("Recursion Timeout")
	if ( safeToPlace( startingBoard, emptyCell, num) ) {
	startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = num // If safe to place number, place it
	// Recursively call the fill function to place num in next empty cell
	if ( fillPuzzle(startingBoard) ) return startingBoard
	// If we were unable to place the future num, that num was wrong. Reset it and try next value
	startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = 0
	}
	}
	return false // If unable to place any number, return false, which triggers previous round to go to next num
	}

	const newSolvedBoard = _ => {
	const newBoard = BLANK_BOARD.map(row => row.slice() ) // Create an unaffiliated clone of a fresh board
	fillPuzzle(newBoard) // Populate the board using backtracking algorithm
	return newBoard
	}

	/*--------------------------------------------------------------------------------------------
	--------------------------------- Generate Playable Board ------------------------------------
	--------------------------------------------------------------------------------------------*/

	const pokeHoles = (startingBoard, holes) => {
	const removedVals = []

	while (removedVals.length < holes) {
	const val = Math.floor(Math.random() * 81) // Value between 0-81
	const randomRowIndex = Math.floor(val / 9) // Integer 0-8 for row index
	const randomColIndex = val % 9

	if (!startingBoard[ randomRowIndex ]) continue // guard against cloning error
	if ( startingBoard[ randomRowIndex ][ randomColIndex ] == 0 ) continue // If cell already empty, restart loop

	removedVals.push({ // Store the current value at the coordinates
	rowIndex: randomRowIndex,
	colIndex: randomColIndex,
	val: startingBoard[ randomRowIndex ][ randomColIndex ]
	})
	startingBoard[ randomRowIndex ][ randomColIndex ] = 0 // "poke a hole" in the board at the coords
	const proposedBoard = startingBoard.map ( row => row.slice() ) // Clone this changed board

	// Attempt to solve the board after removing value. If it cannot be solved, restore the old value.
	// and remove that option from the list
	if ( !fillPuzzle( proposedBoard ) ) {
	startingBoard[ randomRowIndex ][ randomColIndex ] = removedVals.pop().val
	}
	}
	return [removedVals, startingBoard]
	}

	/*--------------------------------------------------------------------------------------------
	--------------------------------- Initialize -------------------------------------
	--------------------------------------------------------------------------------------------*/

	function newStartingBoard (holes) {
	// Reset global iteration counter to 0 and Try to generate a new game.
	// If counter reaches its maximum limit in the fillPuzzle function, current attemp will abort
	// To prevent the abort from crashing the script, the error is caught and used to re-run
	// this function
	try {
	counter = 0
	let solvedBoard = newSolvedBoard()

	// Clone the populated board and poke holes in it.
	// Stored the removed values for clues
	let [removedVals, startingBoard] = pokeHoles( solvedBoard.map ( row => row.slice() ), holes)

	return [removedVals, startingBoard, solvedBoard]

	} catch (error)
	return newStartingBoard(holes)
	}
	}

	// The board will be completely solved once for each item in the empty cell list.
	// The empty cell array is rotated on each iteration, so that the order of the empty cells
	// And thus the order of solving the game, is different each time.
	// The solution for each attempt is pushed to a possibleSolutions array as a string
	// Multiple solutions are identified by taking a unique Set from the possible solutions
	// and measuring its length. If multiple possible solutions are found at any point
	// If will return true, prompting the pokeHoles function to select a new value for removal.

	function multiplePossibleSolutions (boardToCheck) {
	const possibleSolutions = []
	const emptyCellArray = emptyCellCoords(boardToCheck)
	for (let index = 0; index < emptyCellArray.length; index++) {
	// Rotate a clone of the emptyCellArray by one for each iteration
	emptyCellClone = [...emptyCellArray]
	const startingPoint = emptyCellClone.splice(index, 1);
	emptyCellClone.unshift( startingPoint[0] )
	thisSolution = fillFromArray( boardToCheck.map( row => row.slice() ) , emptyCellClone)
	possibleSolutions.push( thisSolution.join() )
	if (Array.from(new Set(possibleSolutions)).length > 1 ) return true
	}
	return false
	}

	// This will attempt to solve the puzzle by placing values into the board in the order that
	// the empty cells list presents
	function fillFromArray(startingBoard, emptyCellArray) {
	const emptyCell = nextStillEmptyCell(startingBoard, emptyCellArray)
	if (!emptyCell) return startingBoard
	for (num of shuffle(numArray) ) {
	pokeCounter++
	if ( pokeCounter > 60_000_000 ) throw new Error ("Poke Timeout")
	if ( safeToPlace( startingBoard, emptyCell, num) ) {
	startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = num
	if ( fillFromArray(startingBoard, emptyCellArray) ) return startingBoard
	startingBoard[ emptyCell.rowIndex ][ emptyCell.colIndex ] = 0
	}
	}
	return false
	}

	// As numbers get placed, not all of the initial cells are still empty.
	// This will find the next still empty cell in the list
	function nextStillEmptyCell (startingBoard, emptyCellArray) {
	for (coords of emptyCellArray) {
	if (startingBoard[ coords.row ][ coords.col ] === 0) return {rowIndex: coords.row, colIndex: coords.col}
	}
	return false
	}

	// Generate array from range, inclusive of start & endbounds.
	const range = (start, end) => {
	const length = end - start + 1
	return Array.from( {length} , ( _ , i) => start + i)
	}

	// Get a list of all empty cells in the board from top-left to bottom-right
	function emptyCellCoords (startingBoard) {
	const listOfEmptyCells = []
	for (const row of range(0,8)) {
	for (const col of range(0,8) ) {
	if (startingBoard[row][col] === 0 ) listOfEmptyCells.push( {row, col } )
	}
	}
	return listOfEmptyCells
	}
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