Exercise 4.6

Given two sets S_1 and S_2, and a number x, describe an O(n log n)
algorithm for finding whether there exists a pair of numbers, one from
S_1 and one from S_2, that add up to x.


Exercise 5-17.

(a) 
Describe an O(n^3) algorithm to determine whether a given
undirected graph contains a triangle or cycle of length 3.

(b) 
Improve the running time to O(|V||E|).


Exercise 5.13 (a)

Find a minimum-size vertex cover in a tree.