# 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}

Original problem

leetcode

array

matrix

dfs

recursion

## Next Post

LeetCode: Happy Number

Aug 24, 2022

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## Previous Post

LeetCode: Validate Binary Search Tree

Aug 20, 2022

Traverse in-order and validate the traversed result

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