Bits — Power of Two

solve(n) — n is a 32-bit signed integer (-2^31 <= n < 2^31). Return true when
n is a power of two (1, 2, 4, 8, …). Zero and negative numbers are not. No loops, no
division, no logarithm: a single expression is enough.

A power of two has exactly one set bit. n & (n - 1) clears the lowest set bit, so it
is 0 only when there was a single one.

Examples

solve(1)    → true
solve(16)   → true
solve(3)    → false
solve(0)    → false
solve(-8)   → false