数组：顺时针打印矩阵

 1 import java.util.ArrayList;
 2 public class Solution {
 3     public ArrayList<Integer> printMatrix(int [][] matrix) {
 4         int row = matrix.length;
 5         int col = matrix[0].length;
 6         ArrayList<Integer> res = new ArrayList<Integer>();
 7         
 8         if(row == 0 && col == 0) {
 9             return res;
10         }
11 
12         int left = 0;
13         int right = col - 1;
14         int top = 0;
15         int bottom = row - 1;
16         
17         while(left <= right && top <= bottom) {
18             //从左到右
19             for(int i = left; i <= right; i++) {
20                 res.add(matrix[top][i]);
21             }
22             //从上到下
23             for(int i = top + 1; i <= bottom; i++) {
24                 res.add(matrix[i][right]);
25             }
26             //从右到左
27             if(top != bottom) {
28                 //防止单行情况
29                 for(int i = right - 1; i >= left; i--) {
30                     res.add(matrix[bottom][i]);
31                 }
32             }
33             //从下到上
34             if(left != right) {
35                 //防止单列情况
36                 for(int i = bottom - 1; i > top; i--) {
37                     res.add(matrix[i][left]);
38                 }
39             }
40             left++; right--; top++; bottom--;
41         }
42         return res;
43     }
44 }