Renamed NQueen file, variables to NQueens, raised RangeError exception (#1162)

Backtracking/NQueens.js

@@ -0,0 +1,67 @@
+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 }