Minimum Unique Array Sum

Given an array of integers, increment any duplicate elements until all elements are unique. The task is to minimize the sum of the array after making all elements unique.

Example:

// With the input
[7, 2, 1, 2, 4, 3] 

// Increment a 2 to get 
[7, 2, 1, 3, 4, 3]
// Increment a 3 to get 
[7, 2, 1, 3, 4, 4]
// Increment a 4 to get 
[7, 2, 1, 3, 4, 5]
// every element is now unique
// => sum : 22