LeetCode - Word Search

最新推荐文章于 2021-07-24 23:29:18 发布

yangyuwei11

最新推荐文章于 2021-07-24 23:29:18 发布

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本文介绍了一种在二维网格中查找指定单词的算法。该算法通过递归地检查相邻单元格来验证单词是否存在，同时确保不重复使用相同的字母单元格。

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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]){//up
			visited[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]){//down
			visited[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]){//left
			visited[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]){//right
			visited[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;
    }
};