[LeetCode] 59. 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 ]]

class Solution {public:    vector<vector<int>> generateMatrix(int n) {        vector<vector<int>> matrix(n, vector<int>(n));        generateMatrix(matrix, 0, n, 1);        return matrix;    }private:    void generateMatrix(vector<vector<int>> &matrix, int startpoint, int n, int baseval) {        if (n <= 0)            return;        else if (n == 1) {            matrix[startpoint][startpoint] = baseval;            return;        } else {            for (int j = startpoint; j < startpoint + n - 1; j++)                matrix[startpoint][j] = baseval++;            for (int i = startpoint; i < startpoint + n - 1; i++)                matrix[i][startpoint + n - 1] = baseval++;            for (int j = startpoint + n - 1; j > startpoint; j--)                matrix[startpoint + n - 1][j] = baseval++;            for (int i = startpoint + n - 1; i > startpoint; i--)                matrix[i][startpoint] = baseval++;            generateMatrix(matrix, startpoint + 1, n - 2, baseval);        }    }};