1. Use the for loop and indexOf method, complexity O(n^
2. Use double loop and splice method, complexity O(n^
3. Double-layer loop, complexity O(n^
4. Use for loops and objects, complexity O(n^
5. Use the filter method and indexOf method, complexity O(n^
6. Use recursion and include, complexity O(n^
7. Use the reduce method and include, complexity O(n^
8. Use Map data structure, complexity O(n)
9. Use filter methods and objects, complexity O(n)
10. Use Set data structure, complexity O(n)
11. Use sorting and double pointers