# 岛屿数量

<p>给你一个由 <code>'1'</code>（陆地）和 <code>'0'</code>（水）组成的的二维网格，请你计算网格中岛屿的数量。</p>

<p>岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。</p>

<p>此外，你可以假设该网格的四条边均被水包围。</p>

<p> </p>

<p><strong>示例 1：</strong></p>

<pre>
<strong>输入：</strong>grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]
<strong>输出：</strong>1
</pre>

<p><strong>示例 2：</strong></p>

<pre>
<strong>输入：</strong>grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
<strong>输出：</strong>3
</pre>

<p> </p>

<p><strong>提示：</strong></p>

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 <= m, n <= 300</code></li>
	<li><code>grid[i][j]</code> 的值为 <code>'0'</code> 或 <code>'1'</code></li>
</ul>


## template

```java

class Solution {
	public int numIslands(char[][] grid) {
		int islandNum = 0;
		for (int i = 0; i < grid.length; i++) {
			for (int j = 0; j < grid[0].length; j++) {
				if (grid[i][j] == '1') {
					infect(grid, i, j);
					islandNum++;
				}
			}
		}
		return islandNum;
	}

	public void infect(char[][] grid, int i, int j) {
		if (i < 0 || i >= grid.length ||
				j < 0 || j >= grid[0].length || grid[i][j] != '1') {
			return;
		}
		grid[i][j] = '2';
		infect(grid, i + 1, j);
		infect(grid, i - 1, j);
		infect(grid, i, j + 1);
		infect(grid, i, j - 1);
	}
}
```

## 答案

```java

```

## 选项

### A

```java

```

### B

```java

```

### C

```java

```