Leetcode: Number of Islands

Question

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

Credits:

Special thanks to @mithmatt for adding this problem and creating all test cases.

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Solution

Analysis

refer to GeeksforGeeks.

“Quotation

This is an variation of the standard problem: “Counting number of connected components in a undirected graph”

“

The code is from 西施豆腐渣.

Code

[code]class Solution(object):
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """

        if grid==[]:
            return 0

        row, col = len(grid), len(grid[0])
        count = 0

        for r in range(row):
            for c in range(col):
                if grid[r][c]=='1':
                    self.search(grid, r, c)
                    count += 1

        return count

    def search(self, grid, r, c):
        if r<0 or r>=len(grid) or c<0 or c>=len(grid[0]) or grid[r][c]=='0':
            return

        grid[r][c] = '0'
        self.search(grid, r-1, c)
        self.search(grid, r+1, c)
        self.search(grid, r, c+1)
        self.search(grid, r, c-1)