codewars: Even Fibonacci Sum

mbuke_repo — Thu, 15 Dec 2022 03:12:53 +0000

This kata I used a pattern common in fibonacci even numbers. In fibonacci series, every number is a factor of some Fibonacci number.

	i	3	4	5	6	7	8	9	10	11	12	...
	Fib(i)	2	3	5	8	13	21	34	55	89	144	...
F a c t o r s	2=Fib(3)	✔️	❌	❌	✔️	❌	❌	✔️	❌	❌	✔️	Every 3^rd Fib number
	3=Fib(4)	❌	✔️	❌	❌	❌	✔️	❌	❌	❌	✔️	Every 4^th Fib number
	5=Fib(5)	❌	❌	✔️	❌	❌	❌	❌	✔️	❌	❌	Every 5^th Fib number
	8=Fib(6)	❌	❌	❌	✔️	❌	❌	❌	❌	❌	✔️	Every 6^th Fib number
	F(k)	...										F(all multiples of k)

As you can see every third number is a multiple of two. So the approach we are going to use is to find fibonacci of multiples of three.

/** num is the number we are going to use to find
    n-th fibonacci. this time we are going to be 
    finding fibonacci of multiples of 3. sum holds
    the sum of all even numbers. prev is holding
    the value from fibonacci calculation 
**/
function solution(max) {
  let num = 3;
  let sum = 0;
  let prev = fibo(num);
  while(prev < max) {
     sum += prev;
     num += 3;
     prev = fibo(num);
  }
  return sum;
}
/* Here I used memoized fibonacci algorithm to reduce time
   and improve efficiency of our algorithm */
function fibo(n, memo={}) {
  if (n < 2) return n;
  if(memo[n]) return memo[n];
  memo[n] = fibo(n - 1, memo) + fibo(n - 2, memo);
  return memo[n];
}

Advantages of using typed useSelector hook

mbuke_repo — Wed, 17 Aug 2022 10:14:00 +0000

One of advantages of using typescript are that it reduces the risk of Bugged Code and more Information/Documentation in Your Codebase. In order to fully embrace these cool features in our react application when using redux we have to use typed react-redux hooks. In this article we are going to explore how we can perform typing on useSelector hook.

When using typed useSelector hook our editor is able to detect properties that are associated with our redux central state.

In order to achieve this we have create a custom hook let's name is useTypedSelector. But before we jump in and implement this cool hook we have to first make some adjustment.

Before we create this hook we have to first determine the type of our redux state i.e properties of the central state. To achieve this we have to perform the following step:

// import all reducers
import {combineReducers, createStore, applyMiddleware} from "redux";
// combine reducers
const reducer = combineReducers({});
export const store =createStore(reducer);
export type RootState = ReturnType<typeof reducer>;

In order to annotate typed useSelector hook we need RootState which represent the type of our redux central state.

So in order to implement our custom typed useSelector hook we need TypedUseSelectorHook interface from react-redux and our RootState for annotation.

import {useSelector, TypedUseSelectorHook}  from "react-redux";
import {RootState} from "../state";

export const useTypedSelector: TypedUseSelectorHook<RootState> = useSelector;

After this, then we can go on and use this hook to select slices of our state we need to use.

DEV Community: mbuke_repo

codewars: Even Fibonacci Sum

Advantages of using typed useSelector hook