Write a program in C to report duplicate

Write a program in C to report duplicate values appearing in an array. A duplicate value only should be reported a single time regardless of how many times it appears in the array.
 

For example, if the values in the array are:
 

1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 4 4 5 6 7 8 9
 

The output should look like this:
 

"Duplicate Values: 1 2 3 4"