package code; /* * 79. Word Search * 题意：在字符数组中搜索字符串 * 难度：Medium * 分类：Array, Backtracking * 思路：回溯法 * Tips：访问过的格子要标记，不能重复访问。回溯法注意回来的时候要重置标志位。向下找的时候直接找4个方向的，回来的时候不用再找了，只需重置标志位。 * 不用mem，因为 ABC ABAD 这种情况，不能仅仅从A一个字符就断定为不为true */ public class lc79 { public static void main(String[] args) { char[][] board = {{'A','B','C','E'},{'S','F','C','S'},{'A','D','E','E'}}; System.out.println(exist(board,"SEE")); } public static boolean exist(char[][] board, String word) { if(board.length==0) return false; boolean [][] flag = 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(search(board,word,i,j,0,flag)) return true; } } return false; } public static boolean search(char[][] board, String word, int i, int j, int sum, boolean[][] flag){ if(sum==word.length()) return true; if(i<0||j<0||i>=board.length||j>=board[0].length) return false; if(board[i][j]!=word.charAt(sum)||flag[i][j]==true) return false; flag[i][j] = true; sum++; boolean r = search(board, word, i, j+1, sum, flag) || search(board, word, i, j-1, sum, flag) || search(board, word, i+1, j, sum, flag) ||search(board, word, i-1, j, sum, flag); flag[i][j] = false; return r; } }