[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 ]
]

https://oj.leetcode.com/problems/spiral-matrix-ii/

思路：按要求输出，注意边界。

public class Solution {
	public int[][] generateMatrix(int n) {
		int[][] mat = new int[n][n];
		if (n <= 0)
			return mat;
		int num = 1;
		int left = 0;
		int right = n - 1;
		int top = 0;
		int bottom = n - 1;
		while (num <= n * n) {
			int i;
			for (i = left; i <= right; i++)
				mat[top][i] = num++;

			for (i = top + 1; i <= bottom; i++)
				mat[i][right] = num++;

			if (top < bottom)
				for (i = right - 1; i >= left; i--)
					mat[bottom][i] = num++;

			if (left < right)
				for (i = bottom - 1; i >= top + 1; i--)
					mat[i][left] = num++;
			top++;
			left++;
			bottom--;
			right--;

		}

		return mat;
	}

	public static void main(String[] args) {
		System.out.println(new Solution().generateMatrix(1));
	}

}

 第二遍记录：边界处理问题参考前一题。