A method for generating a nucleic acid library comprising a plurality of predetermined unique non-random variant target nucleic acids, the method comprising: (a) providing a first plurality of partial double-stranded nucleic acids in a first volume, wherein each of the first plurality of partial double-stranded nucleic acids is a predetermined variant sequence, wherein a first strand of each partial double-stranded nucleic acid in the first plurality has identical single-stranded overhangs, and a second strand of each partial double-stranded nucleic acid in the first plurality has identical single-stranded overhangs, wherein each of the first plurality of partial double-stranded nucleic acids is a predetermined variant sequence that is unique in the first plurality of partial double-stranded nucleic acids; (b) providing a second plurality of partial double-stranded nucleic acids in a second volume, wherein each of the second plurality of partial double-stranded nucleic acids is a predetermined invariant sequence, wherein a first strand of each partial double-stranded nucleic acid in the second plurality has identical single-stranded overhangs and wherein a second strand of each partial double-stranded nucleic acid in the second plurality has identical single-stranded overhangs, wherein the single-stranded overhang of either the first strand or second strand of each partial double-stranded nucleic acid in the second plurality is complementary to the single stranded overhang of either the first strand or the second strand of each partial double-stranded nucleic acid in the first plurality, and wherein each of the second plurality of partial double-stranded nucleic acids is the same predetermined invariant sequence; and (c) assembling the library of nucleic acids by mixing the first plurality of partial double-stranded nucleic acids with the second plurality of partial double-stranded nucleic acids under conditions to hybridize the complementary overhangs to form the library of predetermined unique non-random variant target nucleic acids. (a) providing a first plurality of partial double-stranded nucleic acids in a first volume, wherein each of the first plurality of partial double-stranded nucleic acids is a predetermined variant sequence, wherein a first strand of each partial double-stranded nucleic acid in the first plurality has identical single-stranded overhangs, and a second strand of each partial double-stranded nucleic acid in the first plurality has identical single-stranded overhangs, wherein each of the first plurality of partial double-stranded nucleic acids is a predetermined variant sequence that is unique in the first plurality of partial double-stranded nucleic acids; (b) providing a second plurality of partial double-stranded nucleic acids in a second volume, wherein each of the second plurality of partial double-stranded nucleic acids is a predetermined invariant sequence, wherein a first strand of each partial double-stranded nucleic acid in the second plurality has identical single-stranded overhangs and wherein a second strand of each partial double-stranded nucleic acid in the second plurality has identical single-stranded overhangs, wherein the single-stranded overhang of either the first strand or second strand of each partial double-stranded nucleic acid in the second plurality is complementary to the single stranded overhang of either the first strand or the second strand of each partial double-stranded nucleic acid in the first plurality, and wherein each of the second plurality of partial double-stranded nucleic acids is the same predetermined invariant sequence; and (c) assembling the library of nucleic acids by mixing the first plurality of partial double-stranded nucleic acids with the second plurality of partial double-stranded nucleic acids under conditions to hybridize the complementary overhangs to form the library of predetermined unique non-random variant target nucleic acids.