79. 单词搜索

class Solution 
{
public:
    int dir[4][4]={{-1,0},{1,0},{0,-1},{0,1}};
    
    bool exist(vector<vector<char>>& board, string word) 
    {
        int m=board.size();//几行
        int n=board[0].size();//几列
        vector<vector<bool>> visited(m,vector<bool>(n));//是否被访问过              
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(dfs(i,j,0,board,word,visited)) return true;
            }
        }
        return false;
    }
    
    bool dfs(int x,int y,int index,vector<vector<char>>& board,string &word,vector<vector<bool>>& visited)
    {
        //如果到达最后一个位置，看是否相等
        if(index == word.size() - 1) return board[x][y] == word[index];
        
        if(word[index]==board[x][y])//如果与当前值相等
        {
            visited[x][y]=true;//首先标记为true
            for(int i=0;i<4;i++)//在四个方向上进行
            {
                int new_x=x+dir[i][0];
                int new_y=y+dir[i][1];
                
                //如果new_x与new_y在范围内，并且标记为false，继续递归
                if(new_x >= 0 && new_x < board.size() && new_y >= 0 && new_y < board[0].size() && !visited[new_x][new_y])
                {
                    if(dfs(new_x,new_y,index+1,board,word,visited)) return true;
                }
            }
            visited[x][y]=false;//复位
        }

        return false;
    }
};

 

class Solution 
{
public:
    bool dfs(vector<vector<char>>& board, int i, int j, int l, string word) 
    {
        if (l == word.size()) return true;
        if (i < 0 || i >= board.size() || j < 0 || j >= board[0].size() || board[i][j] != word[l]) return false;

        char tmp = board[i][j];
        board[i][j] = '0';

        if(dfs(board, i - 1, j, l + 1, word) || dfs(board, i, j + 1, l + 1, word) 
        || dfs(board, i + 1, j, l + 1, word) || dfs(board, i, j - 1, l + 1, word)) return true;

        board[i][j] = tmp;
        return false;
    }
    bool exist(vector<vector<char>>& board, string word) 
    {
        //从起始位置开始dfs
        char c = word[0];
        for (int i = 0; i < board.size(); i++) 
        {
            for (int j = 0; j < board[0].size(); j++) 
            {
                if (board[i][j] == c) 
                {
                    if (dfs(board, i, j, 0, word)) return true;
                }

            }
        }
        return false;
    }
};