剑指Offer 顺时针打印矩阵

import java.util.ArrayList;

/**
 * 顺时针打印矩阵
 * 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.
 */
public class JZ019PrintMatrix {

    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        ArrayList<Integer> list1 = new ArrayList<Integer>();
        int cols = matrix[0].length;
        int rows = matrix.length;
        if (matrix == null || cols <= 0 || rows <= 0)
            return null;
        int start = 0;
        while (cols > start * 2 && rows > start * 2) {
            list = printMatrixCore(matrix, cols, rows, start);
            start++;
            for (int i = 0; i < list.size(); i++) {
                list1.add(list.get(i));
            }
        }
        return list1;
    }

    private ArrayList<Integer> printMatrixCore(int[][] m, int cols, int rows, int start) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        int endX = cols - 1 - start; // lie
        int endY = rows - 1 - start; // hang
        for (int i = start; i <= endX; i++) {
            list.add(m[start][i]);
        }
        if (start < endY) {
            for (int i = start + 1; i <= endY; i++) {
                list.add(m[i][endX]);
            }
        }
        if (start < endX && start < endY) {
            for (int i = endX - 1; i >= start; i--) {
                list.add(m[endY][i]);
            }
        }
        if (start < endX && start < endY - 1) {
            for (int i = endY - 1; i >= start + 1; i--) {
                list.add(m[i][start]);
            }
        }
        return list;
    }

}