1. 11849 CD (efficient data structure important; also use BufferedReader in Java)
2. 10954 Add All (dequeue the two smallest addends)
3. 11995 I Can Guess the Data Structure! (good practice simulating three common data structures: stack, queue, and priority queue)
4. 00514 Rails
5. 11503 Virtual Friends
6. 11926 Multitasking (Halim says use a Fenwick Tree)
7. 11235 Frequent Values (use Segment Tree with careful mapping to compute Range Maximum Query, good luck)
8. 11402 Ahoy, Pirates! (modify Segment Tree to support updates, double good luck)

Contest page: here.