Created
February 11, 2020 13:37
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Solution to Codewars kata "Snake Collision" https://www.codewars.com/kata/5ac616ccbc72620a6a000096/javascript
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| // @ts-check | |
| /** | |
| * @param {Array<{ x: number, y: number }>} body snake body coords | |
| * @param {{ x: number, y: number }} cell snake cell to check with | |
| * @returns {{ x: number, y: number }} coords of the cell where collision occured(if any) | |
| */ | |
| function findCollision(body, cell) { | |
| const { x: x1, y: y1 } = cell; | |
| return body.find(({ x: x0, y: y0 }) => (x0 === x1 && y0 === y1)); | |
| } | |
| /** | |
| * @param {{ x: number, y: number }} cell snake body coords | |
| * @param {[number, number]} limits | |
| * @returns {boolean} | |
| */ | |
| function doesCollideWithBorders(cell, limits) { | |
| const [ xMax, yMax ] = limits; | |
| const { x, y } = cell; | |
| return ( | |
| x < 0 || y < 0 || | |
| x >= xMax || y >= yMax | |
| ); | |
| } | |
| /** | |
| * @param {string[]} field | |
| * @param {{ x: number, y: number }} coords | |
| * @param {string} char | |
| */ | |
| function printCell(field, coords, char) { | |
| const row = field[coords.y].split(''); | |
| row[coords.x] = char; | |
| field[coords.y] = row.join(''); | |
| } | |
| /** | |
| * @param {{ x: number, y: number }[]} snake | |
| * @param {string[]} field | |
| */ | |
| function printSnakeToField(snake, field) { | |
| for (let cell of snake) { | |
| printCell(field, cell, 'o') | |
| } | |
| } | |
| /** | |
| * Moves cell in a direction by 1 point | |
| * @param {{ x: number, y: number }} cell | |
| * @param {string} direction | |
| * @returns {{ x: number, y: number }} | |
| */ | |
| function moveCell(cell, direction) { | |
| const { x: x0, y: y0 } = cell; | |
| switch(direction) { | |
| case 'U': return { x: x0, y: y0 - 1 }; | |
| case 'D': return { x: x0, y: y0 + 1 }; | |
| case 'L': return { x: x0 - 1, y: y0 }; | |
| case 'R': return { x: x0 + 1, y: y0 }; | |
| } | |
| } | |
| /** | |
| * @param {string[]} field game field representation | |
| * @param {string} moves snake moves | |
| * @param {number} mvs ? | |
| * @returns {[number, number, number] | number} [x, y, N] | |
| * x, y - coords of the cell where a collision ocurred | |
| * N - number of steps before the collision occured | |
| */ | |
| function snakeCollision(field, moves, mvs=1) { | |
| /** @type [number, number] */ | |
| const FIELD_LIMITS = [ field[0].length, field.length ]; | |
| let snake = [ { x: 0, y: 0 }, { x: 1, y: 0 }, { x: 2, y: 0 } ]; | |
| let stepsTracked = 0; | |
| let snakeMoves = moves; | |
| // prepend default direction to get better structure for moves | |
| if (/[A-Z]/.test(moves[0]) === false) { | |
| snakeMoves = `R ${moves}`; | |
| } | |
| const moveSteps = snakeMoves.split(/\s/).reduce((_moves, move, i, allMoves) => { | |
| if (/[A-Z]/.test(move)) { | |
| const steps = Number(allMoves[i + 1]); | |
| _moves.push({ direction: move, steps }); | |
| } | |
| return _moves; | |
| }, []); | |
| for (let {direction, steps} of moveSteps) { | |
| let step = 0; | |
| while(step < steps) { | |
| stepsTracked++; | |
| const head = snake[snake.length - 1]; | |
| const nextCell = moveCell(head, direction); | |
| const collision = findCollision(snake, nextCell); | |
| if (collision != null) { | |
| const { x, y } = collision; | |
| return [ x, y, stepsTracked ]; | |
| } | |
| if (doesCollideWithBorders(nextCell, FIELD_LIMITS)) { | |
| const { x, y } = head; | |
| return [ x, y, stepsTracked ]; | |
| } | |
| const fieldCell = field[nextCell.y][nextCell.x]; | |
| if (fieldCell == '$') { | |
| // remove food token from the field | |
| printCell(field, nextCell, '-'); | |
| } else { | |
| // If next snake cell is not a food cell - remove snake tail | |
| const removedCell = snake.shift(); | |
| printCell(field, removedCell, '-'); | |
| } | |
| printSnakeToField(snake, field); | |
| field = field; | |
| snake.push(nextCell); | |
| step++; | |
| }; | |
| } | |
| return -1; | |
| } | |
| if (require) { | |
| const { runTests } = require('./test'); | |
| runTests(snakeCollision); | |
| } |
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