解題思路：
就是一圈一圈的加數字，分別上、右、下、左的加

提交程式碼：

class Solution {
	public int[][] generateMatrix(int n) {
		int[][] ans = new int[n][n];

		int cntUp = (int) Math.ceil(n / 2.0);
		int cntLeft = cntUp, cntRight = n / 2, cntBottom = n / 2;
		int pUp = 0, pRight = 0, pBottom = 0, pLeft = 0;
		int num = 1;

		while
 
 (pUp < cntUp) {
			// add up
			for (int j = pUp; j < n - pUp; j++)
				ans[pUp][j] = num++;

			// add right
			if (pRight < cntRight) {
				for (int j = pRight + 1; j < n - 1 - pRight; j++)
					ans[j][n-1-pRight] = num++;
			}

			// add bottom
			if (pBottom < cntBottom) {
				for (int
 
 j = n - 1 - pBottom; j >= pBottom; j--)
					ans[n - 1 - pBottom][j] = num++;
			}

			// add left
			if (pLeft < cntLeft) {
				for (int j = n - 2 - pLeft; j >= 1 + pLeft; j--)
					ans[j][pLeft] = num++;
			}
			pUp++;pBottom++;pRight++;pLeft++;
		}
		return ans;
	}
}

執行結果：