顺时针打印矩阵-剑指Offer

Posted 2020-07-30 RosenDing

顺时针打印矩阵

题目描述

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.

思路

1. 整体是按着一圈一圈打印，需要找到循环继续的条件：columns > startX * 2并且rows > startY * 2
2. 注意打印每圈的时候，四个边的打印循环起始条件

代码

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
       if (matrix == null) {
	    	   return null;
	       }
	       ArrayList<Integer> list = new ArrayList<Integer>();
	       int rows = matrix.length;
	       int columns = matrix[0].length;
	       int start = 0;
	       while (rows > start * 2 && columns > start * 2) {
	    	   int endX = columns - 1 - start;
	    	   int endY = rows - 1 - start;
	    	   for (int i = start; i <= endX; i++) {
	    		  list.add(matrix[start][i]); 
	    	   }
	    	   if (start < endY) {
	    		   for (int i = start + 1; i <= endY; i++) {
	    			   list.add(matrix[i][endX]);
	    		   }
	    	   }
	    	   if (start < endX && start < endY) {
	    		   for (int i = endX - 1; i >= start; i--) {
	    			   list.add(matrix[endY][i]);
	    		   }
	    	   }
	    	   if (start < endX && start < endY - 1) {
	    		   for (int i = endY - 1; i >= start + 1; i--) {
	    			   list.add(matrix[i][start]);
	    		   }
	    	   }
	    	   start++;
	       }
	       return list;
    }
}