Leetcode java Word Search2

/**

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.

*/

For this problem I need to return true or false in the current loop, I can not wait until next loop. cause it program may not enter the next loop. so we need to judge in this loop

Also For backtracking, this program is to set visited array from true to false

public class Solution {
public boolean exist(char[][] board, String word) {
int length = word.length();
if(length <= 0)
return true;
int rowNum = board.length;
if(rowNum == 0)
return false;
int columnNum = board[0].length;
if(columnNum == 0)
return false;
boolean[][] visited = new boolean[rowNum][columnNum];
for(int i = 0; i < rowNum; i++){
for(int j = 0; j < columnNum; j++){
if(helper(word, 0, board, i, j,visited))
return true;
}
}
return false;
}
public boolean helper(String s, int start, char[][]board, int row, int column,boolean[][] visited){
int length = s.length();

if(visited[row][column])
return false;
if(s.charAt(start) != board[row][column])
return false;
visited[row][column] = true;

if(start+1 >= length){
visited[row][column] = false;
return true;
}
int rowNum = board.length;
int columnNum = board[0].length;
if(row + 1< rowNum && helper(s,start + 1,board, row+1,column,visited)){
visited[row][column] = true;
return true;
}
if(row - 1>= 0 && helper(s,start + 1,board, row-1,column,visited)){
visited[row][column] = false;
return true;
}
if(column + 1< columnNum && helper(s,start + 1,board, row,column + 1,visited)){
visited[row][column] = false;
return true;
}
if(column - 1>= 0 && helper(s,start + 1,board, row,column - 1,visited)){
visited[row][column] = false;
return true;
}
visited[row][column] = false;
return false;
}
}