Number of Islands LeetCode solution in JavaScript

1
/**
2
 * @param {character[][]} grid
3
 * @return {number}
4
 */
5
var numIslands = function (grid) {
6
  const directions = [
7
    [1, 0],
8
    [0, 1],
9
    [-1, 0],
10
    [0, -1],
11
  ];
12
  let islandCount = 0;
13

14
  for (let rowIndex = 0; rowIndex < grid.length; rowIndex++) {
15
    for (let colIndex = 0; colIndex < grid[0].length; colIndex++) {
16
      const node = grid[rowIndex][colIndex];
17

18
      // Don't bother with water
19
      if (node === "0") continue;
20

21
      // Once we encounter land, try to get all
22
      // the connected land from the current land.
23
      // Once we get all the land connected from
24
      // the current land, mark them as water so
25
      // that it would disregarded by the main loop.
26
      islandCount++;
27

28
      const connectedLandStack = [[rowIndex, colIndex]];
29

30
      while (connectedLandStack.length > 0) {
31
        const [row, col] = connectedLandStack.pop();
32

33
        // change the land to water
34
        grid[row][col] = "0";
35

36
        for (const direction of directions) {
37
          // To get all the connected land we need to check
38
          //  all directions (left, right, top, bottom)
39
          const newNode = [row + direction[0], col + direction[1]];
40
          const newNodeValue = grid[newNode[0]]?.[newNode[1]];
41

42
          // We only care about the connected lands
43
          if (newNodeValue === undefined || newNodeValue === "0") {
44
            continue;
45
          }
46

47
          connectedLandStack.push(newNode);
48
        }
49
      }
50
    }
51
  }
52

53
  return islandCount;
54
};