LintCode-Word Search II

Given a matrix of lower alphabets and a dictionary. Find all words in the dictionary that can be found in the matrix. A word can start from any position in the matrix and go left/right/up/down to the adjacent position.

Example

Given matrix:

doaf
agai
dcan

and dictionary:

{"dog", "dad", "dgdg", "can", "again"}

 

return {"dog", "dad", "can", "again"}

 

Analysis:

DFS. For every word in the list, check every position of board, if the char at some position matches the first char in the word, then start a DFS at this position.

 

Solution:

 public class Solution {
     /**
      * @param board: A list of lists of character
      * @param words: A list of string
      * @return: A list of string
      */
     public ArrayList<String> wordSearchII(char[][] board, ArrayList<String> words) {
         ArrayList<String> res = new ArrayList<String>();
         if (board.length==0) return res;
         int rowNum = board.length;
         if (board[0].length==0) return res;
         int colNum = board[0].length;

         for (int i=0;i<words.size();i++){
             String word = words.get(i);
             if (word.length()==0) continue;
             for (int j=0;j<rowNum;j++){
                 boolean valid = false;
                 for (int k=0;k<colNum;k++)
                     if (board[j][k]==word.charAt(0)){
                         boolean[][] visited = new boolean[rowNum][colNum];
                         for (int p = 0;p<rowNum;p++)
                             Arrays.fill(visited[p],false);
                         valid = isValidWord(board,visited,word,0,j,k);
                         if (valid){
                             res.add(word);
                             break;
                         }
                     }
                 if (valid) break;
             }
         }

         return res;
     }

     public boolean isValidWord(char[][] board, boolean[][] visited, String word, int pos, int x, int y){
         if (x<0 || x>=board.length || y<0 || y>=board[0].length) return false;
         if (word.charAt(pos)!=board[x][y] || visited[x][y]) return false;

         if (pos==word.length()-1)
                 return true;

         visited[x][y] = true;
         if (isValidWord(board,visited,word,pos+1,x+1,y) || isValidWord(board,visited,word,pos+1,x-1,y) || isValidWord(board,visited,word,pos+1,x,y+1) || isValidWord(board,visited,word,pos+1,x,y-1))
             return true;
         else {
             visited[x][y]=false;
             return false;
         }
     }
 }