Algorithms—79.Word Search

思路：需要记录原来走的路径，之前写的方法是用map来装，耗时太长，参考了下别人的方法。

public class Solution {
public boolean exist(char[][] board, String word) {
if (word==null||word.length()==0||board==null||board.length==0) {
return false;
}
char[] ch=word.toCharArray();
int length=ch.length;
int m=board.length;
int n=board[0].length;
boolean[][] flag=new boolean[m]
;
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
if (board[i][j]==ch[0]&&f(board,ch,0,i,j,length,m,n,flag)) {
return true;
}
}
}
return false;
}
public boolean f(char[][] board,char[] ch,int level,int x,int y,int length,int m,int n,boolean[][] flag){
if (level==length) {
return true;
}
if (x<0||x>=m||y<0||y>=n||flag[x][y]||board[x][y]!=ch[level]) {
return false;
}
flag[x][y]=true;
if (f(board,ch,level+1,x+1,y,length,m,n,flag)) {
return true;
}
if (f(board,ch,level+1,x-1,y,length,m,n,flag)) {
return true;
}
if (f(board,ch,level+1,x,y+1,length,m,n,flag)) {
return true;
}
if (f(board,ch,level+1,x,y-1,length,m,n,flag)) {
return true;
}
flag[x][y]=false;
return false;
}
}