leetcode中等79单词搜索

Posted 2021-06-06 qq_40707462

思路：回溯
用visited数组记录方格是否被遍历过，过后还原

class Solution:
    def exist(self, board: List[List[str]], word: str) -> bool:
        m,n=len(board),len(board[0])
        visited=[]
        directions = [(0, 1), (0, -1), (1, 0), (-1, 0)]

        def dfs(i,j,index):
            if board[i][j]!=word[index]:
                return False
            if index==len(word)-1 :
                return True

            for di,dj in directions:
                newi, newj = i + di, j + dj
                if 0 <= newi < m and 0 <= newj < n and [newi, newj] not in visited:
                    visited.append([i, j])
                    if dfs(newi,newj,index+1):
                        return True
                    visited.pop()


        for i in range(m):
            for j in range(n):
                if dfs(i,j,0):
                    return True
        return False