LeetCode Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

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

与上一题相反，对矩阵赋值，步骤相同。

<pre name="code" class="java">public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] result=new int[n][n];
        int rowstart = 0, rowend = n, colstart = 0, colend = n;
		int num = 0;
		while (num != n * n) {
			// 上行
			for (int i = colstart; i < colend; i++) {
				result[rowstart][i]=num+1;
				num++;
				if (num == n * n)
					return result;
			}
			rowstart++;
			// 右列
			for (int i = rowstart; i < rowend; i++) {
				result[i][colend - 1]=num+1;
				num++;
				if (num == n * n)
					return result;
			}
			colend--;
			// 下行
			for (int i = colend - 1; i >= colstart; i--) {
				result[rowend - 1][i]=num+1;
				num++;
				if (num == n * n)
					return result;
			}
			rowend--;
			// 左列
			for (int i = rowend - 1; i >= rowstart; i--) {
				result[i][colstart]=num+1;
				num++;
				if (num == n * n)
					return result;
			}
			colstart++;
		}
		return result;
    }
}