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January 4, 2021 07:23
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BFS & DFS implementation in JS
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| const board = ['#####B#', '##### #', '#### #', '#### ##', ' ##', 'A######'] | |
| class Node { | |
| constructor(state, parent, action) { | |
| this.state = state | |
| this.parent = parent | |
| this.action = action | |
| } | |
| } | |
| class StackFrontier { | |
| constructor() { | |
| this.frontier = [] | |
| } | |
| add(node) { | |
| this.frontier.push(node) | |
| } | |
| containsState(state) { | |
| return this.frontier.some( | |
| (node) => JSON.stringify(node.state) === JSON.stringify(state), | |
| ) | |
| } | |
| empty() { | |
| return this.frontier.length === 0 | |
| } | |
| remove() { | |
| if (this.empty()) { | |
| console.log('frontier is empty') | |
| return | |
| } else { | |
| const node = this.frontier.pop() | |
| // this.frontier | |
| return node | |
| } | |
| } | |
| } | |
| class QueueFrontier extends StackFrontier { | |
| remove() { | |
| if (this.empty()) { | |
| console.log('frontier is empty') | |
| } else { | |
| const node = this.frontier.shift() | |
| return node | |
| } | |
| } | |
| } | |
| class Hunter { | |
| constructor(board) { | |
| this.height = board.length | |
| const lineLengths = board.map((line) => line.length) | |
| this.width = Math.max(...lineLengths) | |
| // keep track of walls | |
| this.walls = [] | |
| for (let i = 0; i < this.height; i++) { | |
| const row = [] | |
| for (let j = 0; j < this.width; j++) { | |
| if (board[i][j] === 'A') { | |
| this.start = [i, j] | |
| row.push(false) | |
| } else if (board[i][j] === 'B') { | |
| this.goal = [i, j] | |
| row.push(false) | |
| } else if (board[i][j] === ' ') { | |
| row.push(false) | |
| } else { | |
| row.push(true) | |
| } | |
| } | |
| this.walls.push(row) | |
| } | |
| this.solution = null | |
| } | |
| neighbors(state) { | |
| const [row, col] = state | |
| const candidates = [ | |
| ['up', [row - 1, col]], | |
| ['down', [row + 1, col]], | |
| ['left', [row, col - 1]], | |
| ['right', [row, col + 1]], | |
| ] | |
| const result = [] | |
| for (const [action, [r, c]] of candidates) { | |
| if ( | |
| r >= 0 && | |
| r < this.height && | |
| c >= 0 && | |
| c < this.width && | |
| !this.walls[r][c] | |
| ) { | |
| // console.log(this.walls[r][c]) | |
| result.push([action, [r, c]]) | |
| } | |
| } | |
| return result | |
| } | |
| solve() { | |
| this.numExplored = 0 | |
| const start = new Node(this.start, null, null) | |
| const frontier = new StackFrontier() | |
| frontier.add(start) | |
| this.explored = new Set() | |
| // keep looping until solution found | |
| while (true) { | |
| // If nothing left in frontier, then no path | |
| if (frontier.empty()) { | |
| console.log('no solution') | |
| return | |
| } | |
| // choose a node from the frontier | |
| let node = frontier.remove() | |
| this.numExplored += 1 | |
| // If node is the goal, then we have a solution | |
| if (JSON.stringify(node.state) === JSON.stringify(this.goal)) { | |
| // console.log(node.state, this.goal) | |
| const actions = [] | |
| const cells = [] | |
| while (node.parent) { | |
| actions.push(node.action) | |
| cells.push(node.state) | |
| node = node.parent | |
| } | |
| actions.reverse() | |
| cells.reverse() | |
| this.solution = [actions, cells] | |
| console.log('SOLUTION:') | |
| console.log(this.solution) | |
| return | |
| } | |
| // Mark node as explored | |
| this.explored.add(JSON.stringify(node.state)) | |
| // Add neighbors to frontier | |
| for (const [action, state] of this.neighbors(node.state)) { | |
| if ( | |
| !frontier.containsState(state) && | |
| !this.explored.has(JSON.stringify(state)) | |
| ) { | |
| const child = new Node(state, node, action) | |
| frontier.add(child) | |
| } | |
| } | |
| } | |
| } | |
| print() { | |
| const solution = this.solution | |
| ? this.solution[1].map((item) => JSON.stringify(item)) | |
| : null | |
| console.log() | |
| let str = '' | |
| for (const [i, row] of this.walls.entries()) { | |
| for (const [j, col] of row.entries()) { | |
| if (col) { | |
| str += '█' | |
| } else if (JSON.stringify([i, j]) === JSON.stringify(this.start)) { | |
| str += 'A' | |
| } else if (JSON.stringify([i, j]) === JSON.stringify(this.goal)) { | |
| str += 'B' | |
| } else if (solution && solution.includes(JSON.stringify([i, j]))) { | |
| str += '*' | |
| } else { | |
| str += ' ' | |
| } | |
| } | |
| str += '\n' | |
| } | |
| console.log(str) | |
| } | |
| } | |
| var hunter = new Hunter(board) | |
| console.log('Board:') | |
| hunter.print() | |
| console.log('Solving...') | |
| hunter.solve() | |
| console.log('States Explored: ', hunter.numExplored) | |
| console.log('Solution: ') | |
| hunter.print() |
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