LeetCode59.螺旋矩阵II

给你一个正整数n，生成一个包含1到 n 2 n^2 n2所有元素，且元素按顺时针顺序螺旋排列的n x n正方形矩阵matrix。

示例1：

输入：n = 3
输出：[[1,2,3],[8,9,4],[7,6,5]]

示例2：

输入：n = 1
输出：[[1]]

提示

• 1 ⩽ n ⩽ 20 1 leqslant {n}leqslant{20} 1⩽n⩽20

class Solution {
public:
    vector> generateMatrix(int n) {
        vector> res(n, vector(n, 0));
        int loop = n / 2;
        int count = 1;
        int startx = 0, starty = 0;
        int i, j;
        int offset = 1;
        while (loop--) {

            for (j = starty; j < starty + n - offset; j++) {
                res[startx][j] = count++;
            }

            for (i = startx; i < startx + n - offset; i++) {
                res[i][j] = count++;
            }

            for (; j > starty; j--) {
                res[i][j] = count++;
            }

            for (; i > startx; i--) {
                res[i][j] = count++;
            }
            startx++;
            starty++;

            offset += 2;
        }

        if (n%2 == 1) {
            res[n/2][n/2] = count;
        }

        return res;
    }
};