Hash Exercises

Write a method, #word_lengths(string) that, given a sentence, returns a hash of each of the words and their lengths.
```
 word_lengths("hello my good good pal") =
   { 'hello' => 5, 'my' => 2, 'good' => 4, 'pal' => 3 }
```
Write a method, #uniq(array) that returns an array with only the unique values in the array. (Hint: use a hash!) Don't use the Array#uniq method here.
```
 uniq([1, 1, 2, 3])          # ==> [2, 3]
 uniq([1, 3, 4, 3, 2, 5, 4]) # ==> [1, 2, 5]
```
Write a method, #greatest_key_by_val(hash) that takes in a hash with any keys but only integers for values, and returns the key with the largest value.
```
 greatest_key_by_val({ "a" => 5, "b" => 6, "c" => 3 }) # ==> "b"
```

Exercises