Created
September 14, 2022 09:19
-
-
Save kopiro/36288c99fcb35b8957948108ffc3b345 to your computer and use it in GitHub Desktop.
N-Queen with Backtrack
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
function printBoard(board, method = "log") { | |
console[method](board.map((e) => e.join("")).join("\n")); | |
} | |
function createDiagonalMatrix(_) { | |
_.takenDiagonal = []; | |
_.diagonalMatrix = new Array(_.n).fill().map(() => new Array(_.n).fill(-1)); | |
// first row | |
for (let y = 0; y < _.n; y++) { | |
for (let x = 0; x < _.n; x++) { | |
_.takenDiagonal.push(0); | |
const diagonalId = _.takenDiagonal.length - 1; | |
let diagonalIdUsed = false; | |
for (let i = 0; i < _.n; i++) { | |
const _x = x + i; | |
const _y = y + i; | |
if (_x < 0 || _y < 0 || _x >= _.n || _y >= _.n) continue; // skip oob | |
if (_.diagonalMatrix[_y][_x] === -1) { | |
_.diagonalMatrix[_y][_x] = diagonalId; | |
diagonalIdUsed = true; | |
} | |
} | |
if (!diagonalIdUsed) { | |
_.takenDiagonal.pop(); | |
} | |
} | |
} | |
} | |
function nQueenInternal(_) { | |
console.log("start when Y = ", _.cursorY); | |
printBoard(_.board); | |
for (let x = 0; x < _.n; x++) { | |
const y = _.cursorY; | |
console.log(`step`, x, y); | |
if (_.takenX[x]) { | |
console.log(`cant place, X=${x} is taken`); | |
continue; | |
} | |
if (_.takenDiagonal[_.diagonalMatrix[y][x]] > 0) { | |
console.log(`cant place, diagonal=#${_.diagonalMatrix[y][x]} is taken`); | |
continue; | |
} | |
_.board[y][x] = 1; | |
_.takenX[x] = 1; | |
_.takenDiagonal[_.diagonalMatrix[y][x]]++; | |
_.positions.push({ x, y }); | |
console.log("placing queen at ", x, y); | |
printBoard(_.board); | |
_.cursorY++; | |
if (_.cursorY < _.n) { | |
if (nQueenInternal(_)) { | |
return true; | |
} | |
} | |
} | |
// Check success | |
if (_.positions.length === _.n) { | |
console.log("success!"); | |
return true; | |
} | |
// Didn't find a spot for this cursorY, undo last action | |
const pop = _.positions.pop(); | |
if (!pop) { | |
return false; | |
} | |
const { x, y } = pop; | |
console.log(`cant find a spot for Y = ${_.cursorY}, undoing`, pop); | |
_.board[y][x] = 0; | |
_.takenX[x] = 0; | |
_.takenDiagonal[_.diagonalMatrix[y][x]]--; | |
_.cursorY--; | |
printBoard(_.board); | |
return false; | |
} | |
function nQueen(n) { | |
console.warn(`nQueen(${n})`); | |
const board = new Array(n).fill().map(() => new Array(n).fill(0)); | |
const _ = { | |
board, | |
n, | |
cursorY: 0, | |
takenX: {}, | |
positions: [], | |
}; | |
createDiagonalMatrix(_); | |
if (nQueenInternal(_)) { | |
printBoard(_.board, "warn"); | |
return _.positions.map((e) => e.x); | |
} | |
return []; | |
} | |
if (process.argv) { | |
console.warn(nQueen(Number(process.argv[2]))); | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment