Retrieval: when do bits help?

Two problems rebuilt cold, plus the signals that a problem wants bitwise thinking.

Quick check· 5 min

Does this want bits?

Every value in an array appears exactly twice except one, which appears once. You must use constant extra space. What is the approach?

Combine every value with exclusive or; the pairs cancel and the single value remainsTrack seen values in a set, removing on the second sightingSort, then scan for the element without a neighbor equal to itCount occurrences in a hash map and return the one with a count of one

Problem· 15 min

Counting Bits, from scratch

You have solved this one before. Rebuild it from scratch without looking at your old submission. If the approach does not come back within a few minutes, that is the signal that it needs another pass.

Problem· 22 min

Valid Parenthesis String, from scratch

Bit Manipulation

165 / 170

Bit ManipulationLesson 5 of 5About 47 min