顺时针打印矩阵

顺时针打印矩阵

思路：利用四个边界来控制

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
       if(matrix.length == 0) return null;
       ArrayList<Integer> arrayList = new ArrayList<>();
       int left=0,right=matrix[0].length-1,up=0,down=matrix.length-1;
       while(true){
           for (int i=left;i<=right;i++) arrayList.add(matrix[up][i]);
           if(++up>down) break;
           for (int i=up;i<=down;i++) arrayList.add(matrix[i][right]);
           if(--right<left) break;
           for (int i=right;i>=left;i--) arrayList.add(matrix[down][i]);
           if(--down<up) break;
           for (int i=down;i>=up;i--) arrayList.add(matrix[i][left]);
           if(++left>right) break;
       }
        return arrayList;
    }
}