참조
https://enter.tistory.com/165
https://velog.io/@combi_jihoon/%EB%84%A4%ED%8A%B8%EC%9B%8C%ED%81%AC-7-%EB%9D%BC%EC%9A%B0%ED%8C%85-%ED%85%8C%EC%9D%B4%EB%B8%94
https://www.researchgate.net/figure/Distinguishing-safe-routes-from-hop-count-values_fig4_221979955