> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/graphs-bfs-and-dfs/number-of-islands.md).

# Number of Islands

Given a 2d grid map of `'1'`s (land) and `'0'`s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

**Example 1:**

```
Input:
11110
11010
11000
00000

Output: 1
```

**Example 2:**

```
Input:
11000
11000
00100
00011

Output: 3
```

```java
class Solution {
    int[][] directions = { { 1, 0 }, { 0, 1 }, { -1, 0 }, { 0, -1 } };

    public int numIslands(char[][] grid) {
        int m = grid.length;
        if (m == 0)
            return 0;
        int n = grid[0].length;
        boolean visited[][] = new boolean[m][n];
        int ans = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1' && !visited[i][j]) {
                    marker(grid, i, j, visited);
                    ans++;
                }
            }
        }
        return ans;
    }

    public void marker(char[][] grid, int x, int y, boolean[][] visited) {
        if (x >= 0 && x < grid.length && y >= 0 && y < grid[0].length && !visited[x][y] && grid[x][y] == '1') {
            visited[x][y] = true;
            for (int i = 0; i < 4; i++)
                marker(grid, x + directions[i][0], y + directions[i][1], visited);
        }
    }
}
```


---

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