The winner can steal claimer fees, and force him to pay for the gas

Multiple accesses of a mapping/array should use a local variable cache.

+= and -= are more expensive

Uncheck Arithmetic where overflow/underflow impossible

Use `!= 0` rather than `> 0`

Unnecessary If condition in update() of Staking.sol

Use assembly to check for `address(0)`

Use if + custom errors instead of using require + string

Don't initialize `uint/int` variables with default value

Mixed usage of `int`/`uint` with `int256`/`uint256`

Multiple `address` mappings can be combined into a single mapping of an `address` to a `struct`, where appropriate

Using `x >> constant(uint)` with the right shift operator is a more gas-efficient

using x=x+y /x=x-y is more gas efficient than x+=y / x-=y

`++i`/`i++` should be `unchecked{++i}`/`unchecked{i++}` when it is not possible for them to overflow, as is the case when used in `for`- and `while`-loops

Combine Multiple Mapping Address

Use hardcode address instead address(this)

Check price != 0 before interacting with IERC20