class Solution { public: vector<vector<int> > generateMatrix(int n) { // Start typing your C/C++ solution below // DO NOT write int main() function vector<vector<int> > res(n, vector<int>(n)); if (n > 0) { int num = 1; for (int level = 0; level < n / 2; ++level) { for (int i = level; i < n - level; ++i) res[level][i] = num++; for (int i = level + 1; i < n - level; ++i) res[i][n - level - 1] = num++; for (int i = n - level - 2; i >= level; --i) res[n - level - 1][i] = num++; for (int i = n - level - 2; i > level; --i) res[i][level] = num++; } if (n % 2 == 1) res[n / 2][n / 2] = num; } return res; } };