Number of Islands

Medium

Arrays Graphs DFS (Depth-First Search)BFS (Breadth-First Search)Matrix Traversal

Problem

Given an m × n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return 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 surrounded by water.

Constraints

m == grid.length
n == grid[i].length
1 <= m, n <= 300
grid[i][j] is '0' or '1'

Examples

Input:

grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]

Output: 1

All land cells are connected horizontally/vertically, forming one island.

Input:

grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]

Output: 3

Three separate groups of connected land cells — three islands.

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