(Leetcode 2021 刷题计划) 59. 螺旋矩阵 II

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]]

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> matrix(n, vector<int>(n));
        int left = 0, right = n - 1, top = 0, bottom = n - 1;
        int index = 1;
        while (left <= right && top <= bottom) {
            for (int column = left; column <= right; column++, index++) {
                matrix[top][column] = index;
            }
            for (int row = top + 1; row <= bottom; row++, index++) {
                matrix[row][right] = index;
            }
            if (left < right && top < bottom) {
                for (int column = right - 1; column > left; column--, index++) {
                    matrix[bottom][column] = index;
                }
                for (int row = bottom; row > top; row--, index++) {
                    matrix[row][left] = index;
                }
            }
            left++;
            right--;
            top++;
            bottom--;
        }
        return matrix;
    }
};