pub fn contains(&self, x: &T) -> bool
    where
        T: PartialEq<T>,
    {
        self.iter().any(|e| e == x)
    }
Adds an element first in the list.

This operation should compute in *O*(1) time.

# Examples

```
use std::collections::LinkedList;

l
benchmarks/haystacks/code/rust-library.rs