剑指Offer第十九题：顺时针打印矩阵

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.

解答：用标记矩阵来记录已访问的位置
public class Q_19 {

public ArrayList<Integer> printMatrix(int[][] matrix) {
    int sizey = matrix[0].length;//矩阵列边界
    int sizex = matrix.length;//矩阵行边界
    int[][] matrixChooes = new int[matrix.length][matrix[0].length];//访问标记矩阵
    ArrayList<Integer> list = new ArrayList<Integer>();
    int x = 0, y = 0;
    list.add(matrix[0][0]);
    matrixChooes[0][0] = 1;
    int direction = 1;
    while (true) {
        if (direction == 1) {//1是向右，2是向下，3是向左，4是向上
            if (y < sizey - 1 && matrixChooes[x][y + 1] == 0) {//不超过边界且未被访问
                list.add(matrix[x][y + 1]);
                matrixChooes[x][y + 1] = 1;
                y++;
            } else {
                if (x < sizex - 1 && matrixChooes[x + 1][y] == 0) {
                    list.add(matrix[x + 1][y]);
                    matrixChooes[x + 1][y] = 1;
                    x++;
                    direction = 2;//转向
                } else {
                    break;//若是转向后的数值也被访问，则表明所有的数已经被访问
                }
            }
        } else if (direction == 2) {
            if (x < sizex - 1 && matrixChooes[x + 1][y] == 0) {
                list.add(matrix[x + 1][y]);
                matrixChooes[x + 1][y] = 1;
                x++;
            } else {
                if (y > 0 && matrixChooes[x][y - 1] == 0) {
                    list.add(matrix[x][y - 1]);
                    matrixChooes[x][y - 1] = 1;
                    y--;
                    direction = 3;
                } else {
                    break;
                }
            }
        } else if (direction == 3) {
            if (y > 0 && matrixChooes[x][y - 1] == 0) {
                list.add(matrix[x][y - 1]);
                matrixChooes[x][y - 1] = 1;
                y--;
            } else {
                if (x > 0 && matrixChooes[x - 1][y] == 0) {
                    list.add(matrix[x - 1][y]);
                    matrixChooes[x - 1][y] = 1;
                    x--;
                    direction = 4;
                } else {
                    break;
                }
            }
        } else if (direction == 4) {
            if (x > 0 && matrixChooes[x - 1][y] == 0) {
                list.add(matrix[x - 1][y]);
                matrixChooes[x - 1][y] = 1;
                x--;
            } else {
                if (y < sizey - 1 && matrixChooes[x][y + 1] == 0) {
                    list.add(matrix[x][y + 1]);
                    matrixChooes[x][y + 1] = 1;
                    y++;
                    direction = 1;
                } else {
                    break;
                }
            }
        }
    }
    return list;
}
public static void main(String[] args) {
    int[][] matrix = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}};
    int[][] matrix1 = {{}};
    System.out.println(new Q_19().printMatrix(matrix));
}

}