*[Lintcode]Word Search 单词搜索

最新推荐文章于 2020-08-06 09:39:36 发布

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最新推荐文章于 2020-08-06 09:39:36 发布

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分类专栏：算法文章标签： lintcode

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本文介绍了一个二维网格中查找特定单词的算法实现。采用深度优先搜索(DFS)策略，从每个可能的位置开始递归搜索目标单词，确保不重复使用同一字母。通过具体的代码示例展示了如何在给定的字符矩阵中寻找指定的单词。

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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.

Example

Given board =

[
  "ABCE",
  "SFCS",
  "ADEE"
]

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

分析：实现题。双重循环+DFS。以board中每一个字符为起点，查看是否可以找到目标字符串。

public class Solution {
    /**
     * @param board: A list of lists of character
     * @param word: A string
     * @return: A boolean
     */
    public boolean exist(char[][] board, String word) {
        if(word == null || word.length() == 0) return true;
        if(board.length == 0 || board[0].length == 0) return false;
        boolean[][] visit = new boolean[board.length][board[0].length];
        
        for(int i = 0; i < board.length; i++) {
            for(int j = 0; j < board[0].length; j++) {
                if(helper(board, visit, i, j, 0, word)) return true;  
            }
        }
        return false;
    }
    
    boolean helper(char[][] board, boolean[][] visit, int row, int col, int index, String str) {
        if(index >= str.length()) {
            return true;
        }
        
        if(row < 0 || col < 0 || row >= board.length || col >= board[0].length) {
            return false;
        }
        
        if(!visit[row][col] && str.charAt(index) == board[row][col]) {
            visit[row][col] = true;//<-
            boolean res = helper(board, visit, row + 1, col, index + 1, str) || 
                helper(board, visit, row - 1, col, index + 1, str) ||
                helper(board, visit, row, col + 1, index + 1, str) ||
                helper(board, visit, row, col - 1, index + 1, str);
            visit[row][col] = false;//<-
            return res;
        }
        
        return false;
    }
}