renaming files (#401)

* improve file names

* improve file names

Backtracking/KnightTour.js

@@ -0,0 +1,78 @@
+// Wikipedia: https://en.wikipedia.org/wiki/Knight%27s_tour
+
+class OpenKnightTour {
+  constructor (size) {
+    this.board = new Array(size).fill(0).map(() => new Array(size).fill(0))
+    this.size = size
+  }
+
+  getMoves ([i, j]) {
+    // helper function to get the valid moves of the knight from the current position
+    const moves = [
+      [i + 2, j - 1],
+      [i + 2, j + 1],
+      [i - 2, j - 1],
+      [i - 2, j + 1],
+      [i + 1, j - 2],
+      [i + 1, j + 2],
+      [i - 1, j - 2],
+      [i - 1, j + 2]
+    ]
+
+    return moves.filter(([y, x]) => y >= 0 && y < this.size && x >= 0 && x < this.size)
+  }
+
+  isComplete () {
+    // helper function to check if the board is complete
+    return !this.board.map(row => row.includes(0)).includes(true)
+  }
+
+  solve () {
+    // function to find the solution for the given board
+    for (let i = 0; i < this.size; i++) {
+      for (let j = 0; j < this.size; j++) {
+        if (this.solveHelper([i, j], 0)) return true
+      }
+    }
+    return false
+  }
+
+  solveHelper ([i, j], curr) {
+    // helper function for the main computation
+    if (this.isComplete()) return true
+
+    for (const [y, x] of this.getMoves([i, j])) {
+      if (this.board[y][x] === 0) {
+        this.board[y][x] = curr + 1
+        if (this.solveHelper([y, x], curr + 1)) return true
+        // backtracking
+        this.board[y][x] = 0
+      }
+    }
+    return false
+  }
+
+  printBoard () {
+    // utility function to display the board
+    for (const row of this.board) {
+      let string = ''
+      for (const elem of row) {
+        string += elem + '\t'
+      }
+      console.log(string)
+    }
+  }
+}
+
+function main () {
+  const board = new OpenKnightTour(5)
+
+  board.printBoard()
+  console.log('\n')
+
+  board.solve()
+
+  board.printBoard()
+}
+
+main()

Backtracking/NQueen.js

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+class NQueen {
+  constructor (size) {
+    this.board = new Array(size).fill('.').map(() => new Array(size).fill('.'))
+    this.size = size
+  }
+
+  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
+  }
+
+  solve (col = 0) {
+    // function to solve the board
+    if (col >= this.size) { return true }
+
+    for (let i = 0; i < this.size; i++) {
+      if (this.isValid([i, col])) {
+        this.board[i][col] = 'Q'
+
+        if (this.solve(col + 1)) { return true }
+
+        // backtracking
+        this.board[i][col] = '.'
+      }
+    }
+
+    return false
+  }
+
+  printBoard () {
+    // utility function to display the board
+    for (const row of this.board) {
+      console.log(...row)
+    }
+  }
+}
+
+function main () {
+  const board = new NQueen(8)
+
+  board.printBoard()
+  console.log('\n')
+
+  board.solve()
+
+  board.printBoard()
+}
+
+main()

Backtracking/Sudoku.js

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+class Sudoku {
+  // Sudoku Class to hold the board and related functions
+  constructor (board) {
+    this.board = board
+  }
+
+  findEmptyCell () {
+    // Find a empty cell in the board (returns [-1, -1] if all cells are filled)
+    for (let i = 0; i < 9; i++) {
+      for (let j = 0; j < 9; j++) {
+        if (this.board[i][j] === 0) return [i, j]
+      }
+    }
+    return [-1, -1]
+  }
+
+  check ([y, x], value) {
+    // checks if the value to be added in the board is an acceptable value for the cell
+
+    // checking through the row
+    for (let i = 0; i < 9; i++) {
+      if (this.board[i][x] === value) return false
+    }
+    // checking through the column
+    for (let i = 0; i < 9; i++) {
+      if (this.board[y][i] === value) return false
+    }
+
+    // checking through the 3x3 block of the cell
+    const secRow = Math.floor(y / 3)
+    const secCol = Math.floor(x / 3)
+    for (let i = (secRow * 3); i < ((secRow * 3) + 3); i++) {
+      for (let j = (secCol * 3); j < ((secCol * 3) + 3); j++) {
+        if (y !== i && x !== j && this.board[i][j] === value) return false
+      }
+    }
+
+    return true
+  }
+
+  solve () {
+    const [y, x] = this.findEmptyCell()
+
+    // checking if the board is complete
+    if (y === -1 && x === -1) return true
+
+    for (let val = 1; val < 10; val++) {
+      if (this.check([y, x], val)) {
+        this.board[y][x] = val
+        if (this.solve()) return true
+        // backtracking if the board cannot be solved using current configuration
+        this.board[y][x] = 0
+      }
+    }
+    // returning false the board cannot be solved using current configuration
+    return false
+  }
+
+  getSection (row, [start, end]) {
+    return this.board[row].slice(start, end)
+  }
+
+  printBoard () {
+    // helper function to display board
+    for (let i = 0; i < 9; i++) {
+      if (i % 3 === 0 && i !== 0) console.log('- - - - - - - - - - - -')
+      console.log(
+        ...this.getSection(i, [0, 3]), ' | ',
+        ...this.getSection(i, [3, 6]), ' | ',
+        ...this.getSection(i, [6, 9]))
+    }
+  }
+}
+
+function main () {
+  // main function with an example
+  const sudokuBoard = new Sudoku([
+    [3, 0, 6, 5, 0, 8, 4, 0, 0],
+    [5, 2, 0, 0, 0, 0, 0, 0, 0],
+    [0, 8, 7, 0, 0, 0, 0, 3, 1],
+    [0, 0, 3, 0, 1, 0, 0, 8, 0],
+    [9, 0, 0, 8, 6, 3, 0, 0, 5],
+    [0, 5, 0, 0, 9, 0, 6, 0, 0],
+    [1, 3, 0, 0, 0, 0, 2, 5, 0],
+    [0, 0, 0, 0, 0, 0, 0, 7, 4],
+    [0, 0, 5, 2, 0, 6, 3, 0, 0]
+  ])
+
+  sudokuBoard.printBoard()
+
+  console.log('\n')
+  sudokuBoard.solve()
+
+  sudokuBoard.printBoard()
+}
+
+main()