Number of Islands

Given a 2d grid map of '1's (land) and '0's (water), count 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:

11110 11010 11000 00000 Answer: 1

Example 2:

11000 11000 00100 00011 Answer: 3

URL: https://leetcode.com/problems/number-of-islands/

class Solution:
    # @param {boolean[][]} grid a boolean 2D matrix
    # @return {int} an integer
    def numIslands(self, grid):
        if not grid:
            return 0

        row = len(grid)
        col = len(grid[0])
        used = [[False for j in xrange(col)] for i in xrange(row)]

        count = 0
        for i in xrange(row):
            for j in xrange(col):
                if grid[i][j] == '1' and not used[i][j]:
                    self.dfs(grid, used, row, col, i, j)
                    count += 1
        return count

    def dfs(self, grid, used, row, col, x, y):
        if grid[x][y] == '0' or used[x][y]:
            return
        used[x][y] = True

        if x != 0:
            self.dfs(grid, used, row, col, x - 1, y)
        if x != row - 1:
            self.dfs(grid, used, row, col, x + 1, y)
        if y != 0:
            self.dfs(grid, used, row, col, x, y - 1)
        if y != col - 1:
            self.dfs(grid, used, row, col, x, y + 1)