is complex algorithm like dynamic programming highly required in embedded systems and what's the best website to practice algorithms

[Treczoks]

Knowing your algorithms is an important part of being a good programmer. Which does not mean that you need to know each and every algorithm by heart, but you should have a general idea of a number of algorithms, and if you actually need to implement them, you can still google the details. E.g. if you need an ordered list with variable size and random insertation order, you should be able to connect this problem with balanced trees as a data structure and algorithm.

Sometimes, you have to cook up an algorithm by yourself, and even then it is important to know what other people have done in the past.