Find duplicates in N logk time in k sorted arrays

Construct heap of size k using first elements of each array and then keep on adding elements and calling delmin()

Euler cycle in an undirected graph

http://www.graph-magics.com/articles/euler.php

Finding a Hamiltonian cycle is a NP complete problem

Math.abs of -2^31

http://rl337.org/2012/07/31/in-java-when-is-math-abs-negative/