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# 200. Number of Islands

## Description

Given an `m x 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 all surrounded by water.

**Example 1:**

Input:grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ]Output:1

**Example 2:**

Input:grid = [ ["1","1","0","0","0"], ["1","1","0","0","0"], ["0","0","1","0","0"], ["0","0","0","1","1"] ]Output:3

**Constraints:**

`m == grid.length`

`n == grid[i].length`

`1 <= m, n <= 300`

`grid[i][j]`

is`'0'`

or`'1'`

.