LeetCode: Where Will the Ball Fall Solution

If I remember correctly, Alex K. also loves recursion

Approach

Keep in mind for the cases of:

borders
V shape

Implementation

1var findBall = function (grid) {
2  const [m, n] = [grid.length, grid[0].length]
3
4  const recursion = (i, j) => {
5    if (i === m) return j
6
7    // the borders
8    if (j === 0 && grid[i][j] === -1) return -1
9    if (j === n - 1 && grid[i][j] === 1) return -1
10
11    // the \/s
12    if (grid[i][j] === 1 && grid[i][j + 1] === -1) return -1
13    if (grid[i][j] === -1 && grid[i][j - 1] === 1) return -1
14
15    return recursion(i + 1, j + grid[i][j])
16  }
17
18  return Array.from({ length: n }, (_, j) => recursion(0, j))
19}