spiral-algorithm

spiral.js

let arrayOfApps = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24];

const N = [0, -1];
const E = [1, 0];
const S = [0, 1];
const W = [-1, 0];
const EMPTY = `~EMPTY_SIGIL~`

let directions = { N, E, S, W };
let r_directions = { 'N': 'E', 'E': 'S', 'S': 'W', 'W': 'N' };

let rows = 5;
let columns = 5;
// initial 1/2 point
let x = columns + 1 >> 1
let y = rows + 1 >> 1;
let dir = 'N';
let [dx, dy] = directions[dir];
let grid = createGrid(rows, columns);
let result = fillInGrid(grid, x, y);

// *****
//====== RESULT
// *****
console.log(result)

function fillInGrid(grid, x, y) {
  while (true) {
    grid[x-1][y-1] = arrayOfApps.shift();

    // turn right if not visited
    let new_dir = r_directions[dir];
    let [new_dx, new_dy] = directions[new_dir];
    let new_x = x + new_dx;
    let new_y = y + new_dy;

    if (isInBounds(x, y) && grid[new_x-1][new_y-1] === EMPTY) {
      // turn right and continue
      x = new_x;
      y = new_y;
      dx = new_dx;
      dy = new_dy;
      dir = new_dir;
    } else {
      // just keep going in the direction you were headed, maybe continue
      x = x + dx;
      y = y + dy;
      
      if (!isInBounds(x, y)) {
        // nowhere to go. Just return
        return grid;
      }
    }
  }
}

function isInBounds(x, y) {
  return (x >= 0 && x <= columns) && (y >= 0 && y <= rows);
}

function createGrid(w, h) {
  let arr = Array(w).fill(0).map((num, indx) => num + indx);

  return arr.map((x) => {
    return arr.reduce((acc, y) => {
      return acc.concat([EMPTY])   
    }, [])
  })
}