Improved masks for double patterning lithography are described. In one example, conflict spaces between features of a target design are identified. The conflict spaces are represented as nodes of a graph. Connections are inserted between nodes based on a local search. The connections are cut to determine double patterning mask assignment. The connections are extended to form a checkerboard that is then overlayed on the target mask design to split the features of the target mask design for double patterning.