Leetcode剑指0ffer12：矩阵中的路径

一道比较典型的回溯题：深度优先遍历+剪枝
对每个二维数组的字符进行遍历，然后对遍历的字符上下左右进行回溯

class Solution {
    public boolean exist(char[][] board,String word){
        for(int i=0;i<board.length;i++){
            for(int j=0;j<board[0].length;j++){ 
                if(backtracking(board,i,j,0,word)){
                    return true;
                }
            }
        }
        return false;
    }
    public boolean backtracking(char[][] board,int i,int j,int k,String word){
        if(i<0 || i>=board.length || j>=board[0].length || j<0 || board[i][j]!=word.charAt(k)){
            return false;
        }
        if(k==word.length()-1){
            return true;
        }
        board[i][j]='*';
        boolean res= backtracking(board,i-1,j,k+1,word) || backtracking(board,i+1,j,k+1,word)
                || backtracking(board,i,j-1,k+1,word) || backtracking(board,i,j+1,k+1,word);
        board[i][j]=word.charAt(k);
        return res;
    }
}