Once upon a time, there was a young man who was an apprentice in a foreign country. When he learned that his old father was dying at home, he immediately set off on his way. Because of homesickness, only the principle of the shortest line segment between two points is considered, so the straight path A-→B (pictured) covered with gravel is chosen, ignoring the fact that the broken line is long but fast. When he came home panting, the old man swallowed and the young man burst into tears. Neighbors encouraged Xiao. When the gang told him that the old man was dying, he kept talking. "Hu Bugui? Hu Bugui? .."。 This ancient legend has aroused people's thinking. Can this young man go home early? If possible, what route should he choose? This is the "Hu Bugui question" that has been popular for thousands of years.