200. Number of Islands

Medium

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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'.

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        s = set()
        for row in range(len(grid)):
            for col in range(len(grid[0])):
                if grid[row][col] == '1':
                    s.add(self.getKey(row,col))
        count = 0
        while s:
            count += 1
            s = self.removeAllAdjacent(grid,s)
        return count
            
    def removeAllAdjacent(self, grid, s):
        q = []
        q.append(s.pop())
        while q:
            newKey = q.pop(0)
            if newKey in s:
                s.remove(newKey)
            row, col = newKey.split("-")
            row = int(row)
            col = int(col)
            if (row-1) >= 0 and grid[row-1][col] == '1' and self.getKey(row-1,col) in s:
                s.remove(self.getKey(row-1,col))
                q.append(self.getKey(row-1, col))
            if (col-1) >= 0 and grid[row][col-1] == '1' and self.getKey(row,col-1) in s:
                s.remove(self.getKey(row,col-1))
                q.append(self.getKey(row,col-1))
            if (row+1) < len(grid) and grid[row+1][col] == '1' and self.getKey(row+1,col) in s:
                s.remove(self.getKey(row+1,col))
                q.append(self.getKey(row+1, col))
            if (col+1) < len(grid[0]) and grid[row][col+1] == '1' and self.getKey(row,col+1) in s:
                s.remove(self.getKey(row,col+1))
                q.append(self.getKey(row, col+1))
        return s
                
    def getKey(self,row,col):
        return str(row)+"-"+str(col)