LeetCode: Number of Islands Solution

To be consistent, first find out how to make it easy

Approach

After detecting a piece of an island (cell with value 1), recursively spread through all vertical and horizontal directions to discover a full island

Could use any ways to mark the visited state

Implementation

1var numIslands = function (grid) {
2  const [m, n] = [grid.length, grid[0].length]
3
4  let res = 0
5
6  const isValidCell = (i, j) => 0 <= i && i < m && 0 <= j && j < n
7
8  const recursion = (i, j) => {
9    if (isValidCell(i, j) && grid[i][j] === "1") {
10      grid[i][j] = 0
11      recursion(i + 1, j)
12      recursion(i, j + 1)
13      recursion(i - 1, j)
14      recursion(i, j - 1)
15      return
16    }
17  }
18
19  for (let i = 0; i < m; i++) {
20    for (let j = 0; j < n; j++) {
21      if (grid[i][j] === "1") {
22        recursion(i, j)
23        res++
24      }
25    }
26  }
27
28  return res
29}