200、463、695. DFS Island

200 Number of Islands

DFS

class Solution(object):
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        if not grid:
            return 0
        
        count = 0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == '1':
                    self.dfs(grid, i, j)
                    count += 1
        return count

    def dfs(self, grid, i, j):
        if i<0 or j<0 or i>=len(grid) or j>=len(grid[0]) or grid[i][j] != '1':
            return
        grid[i][j] = '#'
        self.dfs(grid, i+1, j)
        self.dfs(grid, i-1, j)
        self.dfs(grid, i, j+1)
        self.dfs(grid, i, j-1)
        

463 Island Perimeter

遍历+判断

class Solution(object):
    def islandPerimeter(self, grid):
        """
        :type grid: List[List[int]]
        :rtype: int
        """
        if not grid:
            return 0
        cnt = 0 
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == 1:
                    cnt  += self.sum_adj(grid,i,j)
        return cnt
    
    def sum_adj(self, grid, i,j):
        adjacent = (i + 1, j), (i - 1, j), (i, j + 1), (i, j - 1),
        res = 0
        for x, y in adjacent:
            if x < 0 or y < 0 or x == len(grid) or y == len(grid[0]) or grid[x][y] == 0:
                res += 1
        return res

695. Max Area of Island

DFS

class Solution(object):
    def maxAreaOfIsland(self, grid):
        """
        :type grid: List[List[int]]
        :rtype: int
        """
        if not grid:
            return 0
        ma = 0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == 1:
                    cnt  = self.dfs(grid,i,j)
                    if cnt > ma:
                        ma = cnt
        return ma
    
    def dfs(self, grid, i,j):
        if (i>=0 and j>=0 and i<len(grid) and j<len(grid[0]) and grid[i][j] == 1):
            grid[i][j] = '#'
            return 1+self.dfs(grid, i+1,j)+self.dfs(grid, i-1,j)+self.dfs(grid, i,j+1)+self.dfs(grid, i,j-1)
        return 0