【深度优先搜索-中等】419. 甲板上的战舰

【题目】

【代码】
【方法1：普通法】修改了board数组

class Solution:
    def countBattleships(self, board: List[List[str]]) -> int:
        cnt=0
        def dfs(x,y):
            if 0<=x<len(board) and 0<=y<len(board[0]) and board[x][y]=="X":
                board[x][y]="."
                return 1 + dfs(x-1,y) + dfs(x+1,y) + dfs(x,y-1) + dfs(x,y+1)
            return 0
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j]=="X":
                    if dfs(i,j):
                        cnt+=1
        return cnt

【方法2】进阶法:不可以修改board数组
遍历board数组，寻找左上角第一个X

class Solution:
    def countBattleships(self, board: List[List[str]]) -> int:
        cnt=0
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j]=="X" and (i==0 or board[i-1][j]==".") and (j==0 or board[i][j-1]=="."):
                    cnt+=1
        return cnt