## partial_sums
### Instructions
Create a function named `parts_sums` , that receives a reference of an array of `u64` , and returns a vector with the partial sums of the received array.
This is how partial sums work:
1- First you split the array in its partitions:
```sh
[1, 2, 3, 4, 5]
|
V
[1, 2, 3, 4, 5]
[1, 2, 3, 4]
[1, 2, 3]
[1, 2]
[1]
[]
```
2- Then you add each partition together:
```sh
[1, 2, 3, 4, 5] = 15
[1, 2, 3, 4] = 10
[1, 2, 3] = 6
[1, 2] = 3
[1] = 1
[] = 0
```
3- So, in conclusion:
```rs
parts_sums(& [1, 2, 3, 4, 5]) // == [15, 10, 6, 3 ,1, 0]
```
### Expected Result
```rs
pub fn parts_sums(arr: & [u64]) -> Vec< 64 > {
}
```
### Example
Here is a program to test your function:
```rs
fn main() {
println!(
"Partial sums of [5, 18, 3, 23] is : {:?}",
parts_sums(& [5, 18, 3, 23])
);
}
```
And its output:
```sh
$ cargo run
Partial sums of [5, 18, 3, 23] is : [49, 26, 23, 5, 0]
$
```
