task1: use BFS to crawl the seed 'https://en.wikipedia.org/wiki/Sustainable_energy' max depth = 5 max num of url = 1000 task2-BFS: use BFS to crawl the seed 'https://en.wikipedia.org/wiki/Sustainable_energy' keyword ’solar’ max depth = 5 max num of url = 1000 task2-DFS: use DFS to crawl the seed 'https://en.wikipedia.org/wiki/Sustainable_energy' keyword ’solar’ max depth = 5 max num of url = 1000 task3: merge two crawl results https://en.wikipedia.org/wiki/Sustainable_energy' 'https://en.wikipedia.org/wiki/Solar_power' rank url