A method comprises (a) receiving data representing a layout of a DPT-layer of an integrated circuit generated by a place and route tool, the layout including a plurality of polygons to be formed in the DPT-layer by a multi-patterning process; (b) receiving at least one identification of a subset of the plurality of polygons that are to be formed in the DPT-layer using the same photomask as each other; (c) constructing a graph of the subset of the plurality of polygons and any intervening polygons of the plurality of polygons, where the subset of the plurality of polygons are represented in the graph by a single node, the graph including connections connecting adjacent ones of the polygons in the graph that are positioned within a threshold distance of each other; and (d) identifying a multi-patterning conflict if any subset of the connections form an odd loop.