矩阵中的路径

/**
用一个状态数组保存之前访问过的字符，然后再分别按上，下，左，右递归
*/
public class Solution {
    public boolean hasPath(char[] matrix, int rows, int cols, char[] str)
    {
        int[] flag = new int[matrix.length];
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < cols; j++) {
                if(helper(matrix, rows, cols, i, j, str, 0, flag)) return true;
            }
        }
        return false;
    }
    public boolean helper(char[] matrix, int rows, int cols, int i, int j, char[] str, int k, int[] flag) {
        int index = i * cols + j;
        if(i<0||i>=rows||j<0||j>=cols||matrix[index]!=str[k]||flag[index]==1) return false;
        if(k == str.length-1) return true;
        flag[index] = 1;
        if(helper(matrix, rows, cols, i-1, j, str, k+1, flag)||
          helper(matrix, rows, cols, i+1, j, str, k+1, flag)||
          helper(matrix, rows, cols, i, j-1, str, k+1, flag)||
          helper(matrix, rows, cols, i, j+1, str, k+1, flag)){
            return true;
        }
        flag[index] = 0;
        return false;
    }
}