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.

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import java.util.ArrayList;public class Solution {    public ArrayList<Integer> printMatrix(int [][] matrix) {       if(matrix == null)            return null;        ArrayList<Integer> list = new ArrayList<>();        int row = matrix.length;        int col = matrix[0].length;        int left = 0, top = 0, right = col-1, bottom = row-1;        while(left <= right && top <= bottom)        {            //从左到右            for(int i = left; i <= right; i++)            {                list.add(matrix[top][i]);            }            //从上到下            for(int j = top+1; j <= bottom; j++)            {                list.add(matrix[j][right]);            }            //从右到左            if(top != bottom)            {                for(int k = right-1; k >= left; k--)                {                    list.add(matrix[bottom][k]);                }            }            //从下到上            if(left != right)            {                for(int l = bottom-1; l > top; l--)//注意边界                {                    list.add(matrix[l][left]);                }            }            //内圈            top++;            left++;            right--;            bottom--;        }        return list;    }}