剑指offerNo19. 顺时针打印矩阵（Java）

题目描述：

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字，例如，如果输入如下4 X 4矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

代码：

package offer;
import java.util.ArrayList;

public class TestNo19 {
    public static void main(String[] args) {
        int[][] a = {{1,2,3,4,5},{1,2,3,4,5},{1,2,3,4,5},{1,2,3,4,5}};
        System.out.println(new TestNo19().printMatrix(a));
    }
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        int rows = matrix.length;
        int cols = matrix[0].length;
        if (matrix == null || cols <= 0 || rows <= 0) {
            return null;
        }
        int start = 0;
        while (cols > start * 2 && rows > start * 2) {
            printMatrixInCircle(list, matrix, cols, rows, start);
            ++start;
        }
        return list;
    }
    private void printMatrixInCircle(ArrayList<Integer> list,int[][] matrix,int cols,int rows,int start){
        int endX = cols-1-start;
        int endY = rows-1-start;
        //从左到右打印一行
        for(int i = start;i<=endX;++i){
            int number = matrix[start][i];
            list.add(number);
        }
        //从上到下打印一列
        if(start < endY){
            for(int i = start+1;i<= endY;++i){
                int number = matrix[i][endX];
                list.add(number);
            }
        }
        //从右向左打印一行
        if(start < endX && start < endY){
            for(int i = endX-1;i>=start;--i){
                int number = matrix[endY][i];
                list.add(number);
            }
        }
        //从下向上打印一列
        if(start < endX && start<endY-1){
            for(int i  = endY-1;i>=start+1;--i){
                int number = matrix[i][start];
                list.add(number);
            }
        }
    }
}