当前位置： 面试刷题>> 岛屿数量(经典算法150题)
### 题目描述
给定一个由 `'1'`（表示陆地）和 `'0'`（表示水域）组成的二维网格，计算网格中岛屿的数量。岛屿总是被水域包围，并且每块岛屿由水平方向和垂直方向上相邻的陆地组成。此外，你可以假设该网格的四条边均被水域包围。
### 示例
**输入**:
```
11110
11010
11000
00000
```
**输出**: 1
**解释**: 只有一个岛屿，由左上角的四个 '1' 组成。
### PHP 示例代码
```php
function numIslands($grid) {
if (empty($grid) || empty($grid[0])) {
return 0;
}
$rows = count($grid);
$cols = strlen($grid[0]);
$count = 0;
for ($i = 0; $i < $rows; $i++) {
for ($j = 0; $j < $cols; $j++) {
if ($grid[$i][$j] == '1') {
dfs($grid, $i, $j);
$count++;
}
}
}
return $count;
}
function dfs(&$grid, $i, $j) {
$rows = count($grid);
$cols = strlen($grid[0]);
if ($i < 0 || $j < 0 || $i >= $rows || $j >= $cols || $grid[$i][$j] != '1') {
return;
}
$grid[$i][$j] = '#'; // 标记为已访问
dfs($grid, $i - 1, $j); // 上
dfs($grid, $i + 1, $j); // 下
dfs($grid, $i, $j - 1); // 左
dfs($grid, $i, $j + 1); // 右
}
// 示例用法
$grid = [
"11110",
"11010",
"11000",
"00000"
];
echo numIslands($grid); // 输出: 1
```
### Python 示例代码
```python
def numIslands(grid):
if not grid or not grid[0]:
return 0
rows, cols = len(grid), len(grid[0])
count = 0
for i in range(rows):
for j in range(cols):
if grid[i][j] == '1':
dfs(grid, i, j)
count += 1
return count
def dfs(grid, i, j):
rows, cols = len(grid), len(grid[0])
if i < 0 or j < 0 or i >= rows or j >= cols or grid[i][j] != '1':
return
grid[i][j] = '#' # 标记为已访问
dfs(grid, i - 1, j) # 上
dfs(grid, i + 1, j) # 下
dfs(grid, i, j - 1) # 左
dfs(grid, i, j + 1) # 右
# 示例用法
grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
]
print(numIslands(grid)) # 输出: 1
```
### JavaScript 示例代码
```javascript
function numIslands(grid) {
if (!grid.length || !grid[0].length) {
return 0;
}
let rows = grid.length;
let cols = grid[0].length;
let count = 0;
for (let i = 0; i < rows; i++) {
for (let j = 0; j < cols; j++) {
if (grid[i][j] === '1') {
dfs(grid, i, j);
count++;
}
}
}
return count;
}
function dfs(grid, i, j) {
const rows = grid.length;
const cols = grid[0].length;
if (i < 0 || j < 0 || i >= rows || j >= cols || grid[i][j] !== '1') {
return;
}
grid[i][j] = '#'; // 标记为已访问
dfs(grid, i - 1, j); // 上
dfs(grid, i + 1, j); // 下
dfs(grid, i, j - 1); // 左
dfs(grid, i, j + 1); // 右
}
// 示例用法
const grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
];
console.log(numIslands(grid)); // 输出: 1
```
这些示例代码均使用了深度优先搜索（DFS）算法来遍历并标记岛屿中的每个陆地，从而计算出岛屿的总数。