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Walkthrough and analysis
Trace Brian Kernighan's trick on n = 12 (binary: 1100).
Iteration 1: n & (n-1) = 1100 & 1011 = 1000. count = 1. Iteration 2: n & (n-1) = 1000 & 0111 = 0000. count = 2. n = 0. Done.
Answer: set bits.
Compare to checking all bits: 12 in binary is 1100. Two 1s.
Brian Kernighan: where is number of set bits. Basic approach: . Both are for fixed-width integers. Space: .
