LeetCode - Word Search

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Given a 2D board and a word, find if the word exists in the grid.

The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.

For example,
Given board =

[  ["ABCE"],  ["SFCS"],  ["ADEE"]]
word = "ABCCED", -> returns true,
word = "SEE", -> returns true,
word = "ABCB", -> returns false.

class Solution {public:    bool exist(vector<vector<char> >& board, vector<vector<bool> >& visited, const string& word,int index,int row,int col){bool existed=false;if(index==word.size()){return !existed;}if(row>0&&!visited[row-1][col]&&board[row-1][col]==word[index]){//upvisited[row-1][col]=true;existed=exist(board,visited,word,index+1,row-1,col);if(existed){return existed;}visited[row-1][col]=false;}if(row<board.size()-1&&!visited[row+1][col]&&board[row+1][col]==word[index]){//downvisited[row+1][col]=true;existed=exist(board,visited,word,index+1,row+1,col);if(existed){return existed;}visited[row+1][col]=false;}if(col>0&&!visited[row][col-1]&&board[row][col-1]==word[index]){//leftvisited[row][col-1]=true;existed=exist(board,visited,word,index+1,row,col-1);if(existed){return existed;}visited[row][col-1]=false;}if(col<board[0].size()-1&&!visited[row][col+1]&&board[row][col+1]==word[index]){//rightvisited[row][col+1]=true;existed=exist(board,visited,word,index+1,row,col+1);if(existed){return existed;}visited[row][col+1]=false;}return existed;    }    bool exist(vector<vector<char> > &board, string word) {bool existed=false;       if(board.empty()||board.size()==0||board[0].empty()||board[0].size()==0){return existed;}int m=board.size(),n=board[0].size();vector<vector<bool> > visited(m,vector<bool>(n,false));for(int i=0;i<m;i++){for(int j=0;j<n;j++){if(board[i][j]==word[0]){visited[i][j]=true;existed=exist(board,visited,word,1,i,j);if(existed){return existed;}visited[i][j]=false;}}}return existed;    }};
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