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class NQueens {

constructor (size) {

if (size < 0) {

throw RangeError('Invalid board size')

}

this.board = new Array(size).fill('.').map(() => new Array(size).fill('.'))

this.size = size

this.solutionCount = 0

}

isValid ([row, col]) {

// function to check if the placement of the queen in the given location is valid

// checking the left of the current row

for (let i = 0; i < col; i++) {

if (this.board[row][i] === 'Q') return false

}

// checking the upper left diagonal

for (let i = row, j = col; i >= 0 && j >= 0; i--, j--) {

if (this.board[i][j] === 'Q') return false

}

// checking the lower left diagonal

for (let i = row, j = col; j >= 0 && i < this.size; i++, j--) {

if (this.board[i][j] === 'Q') return false

}

return true

}

placeQueen (row, col) {

this.board[row][col] = 'Q'

}

removeQueen (row, col) {

this.board[row][col] = '.'

}

solve (col = 0) {

if (col >= this.size) {

this.solutionCount++

return true

}

for (let i = 0; i < this.size; i++) {

if (this.isValid([i, col])) {

this.placeQueen(i, col)

this.solve(col + 1)

this.removeQueen(i, col)

}

}

return false

}

printBoard (output = value => console.log(value)) {

if (!output._isMockFunction) {

output('\n')

}

for (const row of this.board) {

output(row)

}

}

}

export { NQueens }