Brush title -4
Depth-first traversal (DFS) and breadth-first traversal (BFS) understanding
1. Depth-first traversal (Depth-First-Search)
2. The breadth-first traversal (Breadth-First-Search)
Reproduced in: https: //juejin.im/post/5ce63d3b6fb9a07eed34d7d1