#269 Count Number of Islands

medium

javascript

blind75

matrix

dfs

Given a 2D grid where:

'1' represents land
'0' represents water

Count the number of islands. An island is:

Formed by connecting adjacent lands horizontally or vertically
Surrounded by water
Edges of the grid are considered water

Constraints:

1 ≤ grid dimensions ≤ 100
grid cells contain only '0' or '1'

Examples:

// Example 1:
const grid1 = [
  ["0", "1", "1", "1", "0"],
  ["0", "1", "0", "1", "0"],
  ["1", "1", "0", "0", "0"],
  ["0", "0", "0", "0", "0"],
];
console.log(numIslands(grid1));
// Output: 1
// Explanation: One island connected horizontally and vertically

// Example 2:
const grid2 = [
  ["1", "1", "0", "0", "1"],
  ["1", "1", "0", "0", "1"],
  ["0", "0", "1", "0", "0"],
  ["0", "0", "0", "1", "1"],
];
console.log(numIslands(grid2));
// Output: 4
// Explanation: Four separate islands