Rotate Matrix

• Time : $O(n^2)$
• Space : $O(n)$

void helper(vector<vector<int>>& A, int l, int r) {
    if(l >= r) return;
    vector<int> row;
    for(int i = l; i <= r; i++) row.push_back(A[l][i]);
    
    for(int i = l, j = r; i <= r; i++,j--) A[l][j] = A[i][l];
    for(int i = l; i <= r; i++) A[i][l] = A[r][i];
    for(int i = l, j = r; i <= r; i++,j--) A[r][i] = A[j][r];
    for(int i = l; i <= r; i++) A[i][r] = row[i-l];
    
    helper(A,l+1,r-1);
}
void Solution::rotate(vector<vector<int> > &A) {
    helper(A,0,A.size() - 1);
}