class Solution {
public:
vector<vector<int> > generateMatrix(int n) {
vector<vector<int> > res(n, vector<int>(n, 0));
int val = 1, p = n;
for (int i = 0; i < n / 2; ++i, p -= 2) {
for (int col = i; col < i + p; ++col)
res[i][col] = val++;
for (int row = i + 1; row < i + p; ++row)
res[row][i + p - 1] = val++;
for (int col = i + p - 2; col >= i; --col)
res[i + p - 1][col] = val++;
for (int row = i + p - 2; row > i; --row)
res[row][i] = val++;
}
if (n % 2 != 0) res[n / 2][n / 2] = val;
return res;
}
};