LeetCode: Unique Paths II Solution

1/**
2 * @param {number[][]} obstacleGrid
3 * @return {number}
4 */
5var uniquePathsWithObstacles = function (obstacleGrid) {
6  const [M, N] = [obstacleGrid.length, obstacleGrid[0].length]
7  const memo = Array.from({ length: M }, _ => Array(N).fill(null))
8
9  const recursion = (i, j) => {
10    if (memo[i][j] !== null) {
11      return memo[i][j]
12    }
13
14    if (obstacleGrid[i][j] === 1) {
15      return 0
16    }
17
18    if (i === M - 1 && j === N - 1) {
19      return 1
20    }
21
22    let numberOfWays = 0
23    if (i < M - 1) {
24      numberOfWays += recursion(i + 1, j)
25    }
26    if (j < N - 1) {
27      numberOfWays += recursion(i, j + 1)
28    }
29
30    return (memo[i][j] = numberOfWays)
31  }
32
33  return recursion(0, 0)
34}