矩阵问题

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.

思路：
一共有上下左右四个边界，走到头就转向，回到起点四个边界缩小，循环为止

public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
      int row = matrix.length;
        int line = matrix[0].length;
        ArrayList<Integer> list = new ArrayList<Integer>();
        int top = 0, left = 0, right = line - 1, bottom = row - 1;
        while (top <= bottom && left <= right) {

             for (int i = left; i <= right; i++) {
                list.add(matrix[top][i]);
             }

             for (int i = top+1; i <= bottom; i++) {
                list.add(matrix[i][right]);
             }

            if(top!=bottom){
            for (int i = right-1; i >= left; i--) {
                list.add(matrix[bottom][i]);
                }
            }
            if(left!=right){
            for(int i=bottom-1;i>top;i--)
            {

                list.add(matrix[i][left]);
            }
            }

              left++;
              top++;
             right--;
            bottom--;

        }
        return list;
    }
}