[leetcode]word search

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.

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 Array Backtracking

class Solution {public:    bool dfs(vector<vector<char> > &board, string word, int i, int j){        int M = board.size();        int N = board[0].size();                if(i < 0 || j < 0 || i >= M || j >= N || board[i][j]!=word[0]) return false;                if(word.size() == 1) return true;                board[i][j] = '#';                bool tmp = dfs(board, word.substr(1,word.size()-1), i-1, j) ||                dfs(board, word.substr(1,word.size()-1), i+1, j) ||                dfs(board, word.substr(1,word.size()-1), i, j-1) ||                dfs(board, word.substr(1,word.size()-1), i, j+1);                board[i][j] = word[0];        return tmp;    }    bool exist(vector<vector<char> > &board, string word) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(board.empty()) return false;        for(int i = 0; i < board.size(); i++){            for(int j = 0; j < board[0].size(); j++){                if(dfs(board, word, i, j)) return true;            }        }                return false;            }};