leetcode 079 word search

最新推荐文章于 2020-12-16 14:14:51 发布

walter1990

最新推荐文章于 2020-12-16 14:14:51 发布

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本文介绍了一个算法，用于在二维字符网格中查找特定单词是否存在。该算法通过递归地检查每个相邻单元格，并确保同一单元格不会被重复使用来实现目标单词的匹配。

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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 =

[
  ['A','B','C','E'],
  ['S','F','C','S'],
  ['A','D','E','E']
]

word = "ABCCED" , -> returns true ,
word = "SEE" , -> returns true ,
word = "ABCB" , -> returns false .

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class Solution {
public:
   bool find(vector<vector<char>> &board, vector<vector<int>> &visited, string word, int row, int col, int cnt, int used) {
		int rows = board.size(), cols = board[0].size();

		if(cnt==word.length()) return true;
		if(row >= rows || col >= cols || row < 0 || col < 0) return false;
		if(visited[row][col] == 1) return false;
		if(board[row][col]!=word[cnt]) return false;
        
        if(used >= rows*cols) return false;
		visited[row][col] = 1;
		used += 1;
		//cout << "row="<<row<<" col=" << col << board[row][col] << endl;
		bool flag1=find(board, visited, word, row+1, col, cnt+1, used);
		if(flag1) return true;
		bool flag2=find(board, visited, word, row, col+1, cnt+1, used);
		if(flag2) return true;
		bool flag3=find(board, visited, word, row-1, col, cnt+1, used);
		if(flag3) return true;
		bool flag4=find(board, visited, word, row, col-1, cnt+1, used);
        if(flag4) return true;
        
        visited[row][col]=0;
        used-=1;
		return false;
		
	}
	bool exist(vector<vector<char>> &board, string word) {
		int rows=board.size(), cols=0, len=word.length();

		if(rows==0) return false;
        if(len==0) return true;
        
		cols = board[0].size();
        bool ret = false;
        vector<vector<int>> visited(rows, vector<int>(cols,0));
		for(int i=0; i < rows; i++) {
		    for(int j=0; j < cols; j++) {
		        if(board[i][j]==word[0]) {
		            ret = find(board, visited, word, i, j, 0, 0);
		            if(ret==true) return true;
		        }
		    }
		}
		
		return false;
	}
};