Given an array of paired integers, write an algorithm to find the integer that is not paired, using constant space.
Sigiloso
XOR them all together. I can't believe this counts as an interview question. In Haskell it is literally one line: findUnpaired = foldr1 Data.Bits.xor This works since: xor is associative and commutative, xor has identity 0, xor of two equal numbers gives 0.