###Palindrome Potential

_A palindrome is a word that reads the same forward, as it does backward_

Write a method called `could_be_palindrome?()`, that takes in String. This method determines whether or not the letters in a String could be re-arranged into a palindrome. Your method should return `true` or `false`

For instance:

```ruby
# tests
could_be_palindrome?("aab")    # true: "aba"
could_be_palindrome?("aabbc")  # true: "abcba"
could_be_palindrome?("aaab")   # false
```

###Substrings

Write a method called `is_substring?`

It shoud take in 2 Strings, in this case words. The first is our original word. The second is what we're checking to see if its a substring or not. "_The catch_" is... your'e NOT allowed to use Ruby's `.include?` method.

For instance:

```ruby
our_word = 'devbootcamp'
is_substring?(our_word, 'boot') # true
is_substring?(our_word, 'camp') # true
is_substring?(our_word, 'code') # false
```

###Stock History

Below are the stock prices for ACME Co. They've been helping out Elmer Fudd and Wile E. Coyote for years! On Day 1, the price was 9, Day 2 it was 4 and so on.

```ruby
acme_stock_prices = [ 9, 4, 2, 1, 3, 6, 15, 13, 8 ]
```

We want to figure out a program for telling us the best time to buy and sell ACME Co. stock. In our example, it would be:

```
- Buy on Day 4
- Sell on Day 7
```

Write a method called `best_prices` that takes in an Array of Integers. Return the days as an Array.

Example:
```ruby
best_prices(acme_stock_prices) # [ 4, 7 ]
```