GOOGLE挑战赛练习题2及答案(500分)

Problem Statement
	A square matrix is a grid of NxN numbers. For example, the following is a 3x3 matrix: 4 3 5 2 4 5 0 1 9 One way to represent a matrix of numbers, each of which is between 0 and 9 inclusive, is as a row-major String. To generate the String, simply concatenate all of the elements from the first row followed by the second row and so on, without any spaces. For example, the above matrix would be represented as "435245019". You will be given a square matrix as a row-major String. Your task is to convert it into a String[], where each element represents one row of the original matrix. Element i of the String[] represents row i of the matrix. You should not include any spaces in your return. Hence, for the above String, you would return {"435","245","019"}. If the input does not represent a square matrix because the number of characters is not a perfect square, return an empty String[], {}.
Definition
	Class: MatrixTool Method: convert Parameters: String Returns: String[] Method signature: String[] convert(String s) (be sure your method is public)

public class MatrixTool
{

        public String[]  convert(String str)
        {
                String[] matrix = null;
                if(str==null || str.length()<1)
                {
                        return matrix;
                }

                int total = str.length();
                double d = total/1.0;
                int len = (int)Math.sqrt(d);

                //check

                for(int i=0;i<total;i++)
                {

                        if(str.charAt(i)>='0' && str.charAt(i)<='9')
                        {
                        }
                        else
                        {
                                System.out.println("invaid charareter.");
                                return matrix;
                        }
                }

 

                if(len*len == total)
                {
                        matrix = new String[len];
                        for(int i=0;i<len;i++)
                        {
                           matrix[i] = "";
                           for(int j=0;j<len;j++)
                           {
                              matrix[i]+= str.charAt(i*len+j);
                           }
                        }

                }
                return matrix;

        }
       
        public static void main(String args[]){
          MatrixTool mt = new MatrixTool();
          String[] temp = mt.convert("435245019");
          for(int i=0;i<temp.length;i++){
            System.out.println(temp[i]);
          }
        }

}