题解 | #顺时针打印矩阵#

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
       ArrayList<Integer> list = new ArrayList<>();
	  //特殊情况
       if(matrix.length==0){
           return list;
       }
       int up = 0;
       int down = matrix.length-1;
       int left = 0;
       int right = matrix[0].length-1;

       while(up<=down&&left<=right){
        //向右
		   for(int i=left;i<=right;i++){
               list.add(matrix[up][i]);
           }
           up++;
           if(up>down){
               break;
           }
		//向下
           for(int i=up;i<=down;i++){
               list.add(matrix[i][right]);
           }
           right--;
           if(left>right){
               break;
           }
		//向左
           for(int i=right;i>=left;i--){
               list.add(matrix[down][i]);
           }
           down--;
           if(down<up){
               break;
           }
		//向上
           for(int i=down;i>=up;i--){
               list.add(matrix[i][left]);
           }
           left++;
           if(left>right){
               break;
           }
       }
       return list;
    }
}