【LeetCode】59. Spiral Matrix II

问题描述

https://leetcode.com/problems/spiral-matrix-ii/#/description

Given an integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

输入一个数n，输出从1到n^2的螺旋排序矩阵。

算法

直接按照从左到右、从上到下、从右到左、从下到上的顺序一个个数的填充数组即可。

代码

public int[][] generateMatrix(int n) {
	    	if(n<=0) return new int[][]{};
	    	int[][] res = new int[n][n];
	    	// 开始填入数字
	    	int rowBegin = 0, rowEnd = n-1;
	    	int colBegin = 0, colEnd = n-1;
	    	int index = 1;
	    	while(rowBegin<=rowEnd || colBegin<=colEnd) {
	    		// 从左到右
	    		for(int i=colBegin;i<=colEnd;i++) {
	    			res[rowBegin][i] = index++;
	    		}
	    		rowBegin++;
	    		// 从上到下
	    		for(int i=rowBegin;i<=rowEnd;i++) {
	    			res[i][colEnd] = index++;
	    		}
	    		colEnd--;
	    		// 从右到左
	    		if(colEnd>=colBegin) {
		    		for(int i=colEnd;i>=colBegin;i--) {
		    			res[rowEnd][i] = index++;
		    		}
	    		}
	    		rowEnd--;
	    		// 从下到上
	    		if(rowEnd >=rowBegin) {
	    			for(int i=rowEnd;i>=rowBegin;i--) {
	    				res[i][colBegin] = index++;
	    			}
	    		}
	    		colBegin++;
	    	}
	    	return res;
	    }

LeetCode解题代码仓库：https://github.com/zgljl2012/leetcode-java