Both techniques prove the same thing (greedy is optimal) but work differently: Exchange: Transform any OPT into G step by step. Stays ahead: Show G is never behind at any step. Use exchange when:
- Swapping is easy to describe. The problem has discrete choices Use stays ahead when:
- There is a natural progress measure. Induction flows easily For activity selection, both work. In practice, choose whichever feels more natural for your problem.