//Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
//
//Example 1:
//
//Input:
//[
 //[ 1, 2, 3 ],
 //[ 4, 5, 6 ],
 //[ 7, 8, 9 ]
//]
//Output: [1,2,3,6,9,8,7,4,5]
//Example 2:
//
//Input:
//[
  //[1, 2, 3, 4],
  //[5, 6, 7, 8],
  //[9,10,11,12]
//]
//Output: [1,2,3,4,8,12,11,10,9,5,6,7]

class SpiralMatrix {
    public List spiralOrder(int[][] matrix) {
        List result = new ArrayList();
        if(matrix == null || matrix.length == 0) {
            return result;
        }
        
        int rowStart = 0;
        int rowEnd = matrix.length - 1;
        int colStart = 0;
        int colEnd = matrix[0].length - 1;
        while(rowStart