For example, we have $T(N) = T(N/2) + T(N/5) + O(N)$. So:$2T(N/2) + O(N) \leq T(N) \leq 2T(N/5) + O(N)$$O(N) \leq T(N) \leq O(N)$. Thus, $T(N) = O(N)$. Is it correct?
Algorithm complexity
algorithm analysis;time complexity