Trace code in your head

When to reach for it

Trace table

When you're not sure what a loop does. Pick a small input that still makes the loop run two or three times.

Check the loop bounds

Every time you write a loop. Trace just the first and the last round, since boundary bugs always live there.

Early return

When the answer is already certain in the middle of the loop. Return inside the loop, and put the "not found" answer after it.

Before you submit

Every time a test fails but your logic feels right. Check these three things first.