Dynamic len(set(a[L:R]))

Problem Number: 
12 345
Type of Problem: 
Single Output Problem
Problem Category: 
Volume 123 (12,300-12,399)
Input: 
0
0
0
Critical Input: 
Random Input: 
Problem Description Link: 
https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=1…
Problem Id: 
12345