//    題目描述
//    輸入一個矩陣，按照從外向裏以順時針的順序依次打印出每一個數字，
//    例如，如果輸入如下矩陣： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
//    則依次打印出數字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.


    public static ArrayList<Integer> printMatrix(int[][] matrix) {
        ArrayList<Integer> arrayList = new ArrayList<Integer>();

        
 
int topLine = 0;
        int firstColumn = 0;
        for (int i = topLine; i < matrix.length - topLine&&firstColumn<matrix[i].length - firstColumn; i++) {
            for (int j = firstColumn; j < matrix[i].length - firstColumn; j++) {
                arrayList.add(matrix[i][j]);

            }
            
 
for (int j = topLine + 1; j < matrix.length - topLine; j++) {
                if (matrix[j].length - firstColumn - 1 < firstColumn) {
                    break;
                }
                arrayList.add(matrix[j][matrix[j].length - firstColumn - 1]);
            }
            for (int j = matrix[i].length - firstColumn - 2; j >= firstColumn; j--) {
                
 
if (topLine >= matrix.length - topLine - 1) {
                    break;
                }
                arrayList.add(matrix[matrix.length - topLine - 1][j]);

            }
            for (int j = matrix.length - topLine - 2; j > topLine; j--) {
                if (firstColumn >= matrix[j].length - firstColumn - 1) {
                    break;
                }
                arrayList.add(matrix[j][firstColumn]);
            }

            topLine++;
            firstColumn++;
        }
        return arrayList;
    }

牛客（19）順時針打印矩陣