在字符网格中搜索单词

Posted 2023-02-22

【中文标题】在字符网格中搜索单词

【英文标题】：search a word in grid of characters

【发布时间】：2019-03-13 18:46:06

【问题描述】：

我正在处理leetcode problem。我想出了以下简单的解决方案，但输出错误。

给定一个二维板和一个单词，找出该单词是否存在于网格中。

单词可以由顺序相邻的字母构成 单元格，其中“相邻”单元格是水平或垂直的单元格 邻接。同一个字母单元格不能多次使用。

对于这个输入：

棋盘：[["a","b"],["c","d"]]

单词：“abcd”

它应该返回 false，但下面的解决方案返回 true。

public static boolean exist(char[][] board, String word) 
    int row = board.length;
    int col = board[0].length;
    Map<Character, Integer> hm = new HashMap<Character, Integer>();
    for (int i = 0; i < row; i++) 
      for (int j = 0; j < col; j++) 
        hm.put(board[i][j], hm.getOrDefault(board[i][j], 0) + 1);
      
    

    char[] words = word.toCharArray();
    for (int i = 0; i < words.length; i++) 
      char x = words[i];
      if (hm.containsKey(x) && hm.get(x) > 0)
        hm.put(x, hm.get(x) - 1);
      else
        return false;
    
    return true;
  

【参考方案1】：

使用 DFS（深度优先搜索）算法：

public boolean exist(char[][] board, String word) 
    int m = board.length;
    int n = board[0].length;

    boolean result = false;
    for(int i=0; i<m; i++)
        for(int j=0; j<n; j++)
           if(dfs(board,word,i,j,0))
               result = true;
           
        
    

    return result;


public boolean dfs(char[][] board, String word, int i, int j, int k)
    int m = board.length;
    int n = board[0].length;

    if(i<0 || j<0 || i>=m || j>=n)
        return false;
    

    if(board[i][j] == word.charAt(k))
        char temp = board[i][j];
        board[i][j]='#';
        if(k==word.length()-1)
            return true;
        else if(dfs(board, word, i-1, j, k+1)
        ||dfs(board, word, i+1, j, k+1)
        ||dfs(board, word, i, j-1, k+1)
        ||dfs(board, word, i, j+1, k+1))
            return true;
        
        board[i][j]=temp;
    

    return false;

【讨论】：

是的，这是一种方法。我在想我的方法有什么问题？

在您的解决方案中，您每次都在查看网格中的每个字母。

【参考方案2】：

这是一种不同的方法，它使用 Java 流。希望对您有所帮助！

import java.util.Arrays;
import java.util.stream.IntStream;

public class WordSearch
     public static void main(String []args)
        final char[][] matrix = 
            'X', 'H', 'A', 'T',
            'X', 'E', 'X', 'X',
            'X', 'L', 'X', 'O',
            'X', 'L', 'X', 'W',
            'C', 'O', 'O', 'L'
        ;

        previewMatrix(matrix);

        String[] searchSequences = "COOL", "HAT", "HELLO", "OWL", "WORLD";

        for (String searchSequence : searchSequences) 
            boolean isWordFound = searchWord(searchSequence, matrix);

            if (isWordFound) 
                System.out.printf("[ PASS ] The character sequence %s has been found in the matrix.\n", searchSequence);
             else 
                System.out.printf("[ FAIL ] The character sequence %s was not found in the matrix.\n", searchSequence);
            
        
     

     private static boolean searchWord(String searchSequence, char[][] matrix) 
         boolean isWordFound = false;
         String rowString = null;

         for (char[] row : matrix) 
             rowString = new String(row);

             if (rowString.contains(searchSequence)) 
                   isWordFound = true;
                   break;
             
         

         if (!isWordFound) 
             int columnsCount = matrix[0].length;
             String colString = null;

             for (int colIndex=0; colIndex < columnsCount; colIndex++) 
                   colString = getColumnContent(matrix, colIndex); 
                   if (colString.contains(searchSequence)) 
                        isWordFound = true;
                        break;
                   
             
         

         return isWordFound;
     

     private static void previewMatrix(char[][] matrix) 
         for (char[] row : matrix) 
            for (char ch : row) 
                System.out.print(ch + " ");
            

            System.out.println();
        

        System.out.println();
     

     private static String getColumnContent(char[][] matrix, int columnIndex) 
         return IntStream
            .range(0, matrix.length)
            .mapToObj(i -> (char) matrix[i][columnIndex])
            .collect(
                StringBuilder::new,
                StringBuilder::appendCodePoint,
                StringBuilder::append)
            .toString();