google 编程挑战赛（2）

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 vector <string>, where each element represents one row of the original matrix. Element i of the vector <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 vector <string>, {}.
Definition
	Class: MatrixTool Method: convert Parameters: string Returns: vector <string> Method signature: vector <string> convert(string s) (be sure your method is public)
Constraints
-	s will contain between 1 and 50 digits, inclusive.
Examples
0)
	"435245019" Returns: {"435", "245", "019" } The example above.
1)
	"9" Returns: {"9" }
2)
	"0123456789" Returns: { } This input has 10 digits, and 10 is not a perfect square.
3)
	"3357002966366183191503444273807479559869883303524" Returns: {"3357002", "9663661", "8319150", "3444273", "8074795", "5986988", "3303524" }

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下面是我的解答#include
#include
#include
using namespace std;
class MatrixTool
{
public:
 MatrixTool(){}
 vector convert(string s);
};
vector MatrixTool::convert(string s)
{
 vector result;
 int n=(int)sqrt(s.size());
 if(s.size()==n*n)
 {
  result.resize(n);
  for(int i=0;i<n;i++)
  {
   result[i]=s.substr(i*n,n);
  }
 }
 return result;
}