@inproceedings{wen-qi2011approximating,
title={Approximating the longest paths in grid graphs},
author={Wen-Qi Zhang, and Yong-Jin Liu},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20160819152545835538265},
booktitle={Theoretical Computer Science},
volume={412},
number={39},
pages={5340},
year={2011},
}

Wen-Qi Zhang, and Yong-Jin Liu. Approximating the longest paths in grid graphs. 2011. Vol. 412. In Theoretical Computer Science. pp.5340. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20160819152545835538265.