CodeWars: Snail Solution

Approach

Keep going in one direction at a time, with the order:

• right
• down
• left
• up
• ..then repeat

Implementation

1snail = function (array) {
2  const n = array[0].length
3
4  const visited = Array.from({ length: n }, _ => Array(n).fill(false))
5  const res = []
6
7  const valid = (row, col) => 0 <= row && row < n && 0 <= col && col < n
8  const canGoUp = (row, col) => valid(row - 1, col) && !visited[row - 1][col]
9  const canGoDown = (row, col) => valid(row + 1, col) && !visited[row + 1][col]
10  const canGoLeft = (row, col) => valid(row, col - 1) && !visited[row][col - 1]
11  const canGoRight = (row, col) => valid(row, col + 1) && !visited[row][col + 1]
12
13  const visit = (row, col) => {
14    res.push(array[row][col])
15    visited[row][col] = true
16  }
17
18  for (let row = 0, col = 0; n > 0; ) {
19    if (canGoRight(row, col)) {
20      while (canGoRight(row, col)) visit(row, col++)
21      continue
22    }
23
24    if (canGoDown(row, col)) {
25      while (canGoDown(row, col)) visit(row++, col)
26      continue
27    }
28
29    if (canGoLeft(row, col)) {
30      while (canGoLeft(row, col)) visit(row, col--)
31      continue
32    }
33
34    if (canGoUp(row, col)) {
35      while (canGoUp(row, col)) visit(row--, col)
36      continue
37    }
38
39    // final cell
40    visit(row, col)
41
42    break
43  }
44
45  return res
46}