When VLSI technology scales down to sub-40nm process node, systematic variation introduced by the lithography is a persistent challenge to the manufacturability. The limitation of the resolution enhancement technologies (RETs) forces people to adopt a regular cell design methodology. In this paper, targeted on 1-D cell design, we use simulation data to analyze the relationship between the line-end gap distribution and printability. Based on the gap distribution preferences, an optimal algorithm is provided to efficiently extend the line ends and insert dummies, which will significantly improve the gap distribution and help printability. Experimental results on 45nm and 32nm processes show that significant improvement can be obtained on edge placement error (EPE).