[编程题]顺时针打印矩阵-JAVA

取数方向是→↓←↑，对应direction的0、1、2、3，当List大小为矩阵元素个数时终止循环，不需要麻烦的条件判断，思路简洁。

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> res = new ArrayList<>();
        int col = matrix.length;
        int row = matrix[0].length;

        int up = 0;
        int down = col - 1;
        int left = 0;
        int right = row - 1;
        int i = 0;
        int direction = 0;
        int size = col * row;
        while(res.size()<size){
            if(direction%4==0){
                for(i=left;i<=right;i++){
                    res.add(matrix[up][i]);
                }
                up++;
            }
            else if(direction%4==1){
                for(i=up;i<=down;i++){
                    res.add(matrix[i][right]);
                }
                right--;
            }
            else if(direction%4==2){
                for(i=right;i>=left;i--){
                    res.add(matrix[down][i]);
                }
                down--;
            }
            else{
                for(i=down;i>=up;i--){
                    res.add(matrix[i][left]);
                }
                left++;
            }
            direction++;
        }
        return res;
    }
}