c# - How to calculate the time complexity of this odd method -

the method is:

list<book> books = new list<book>();  public list<book> shoot() {    foreach(var b in books)    {        bool find = true;        foreach(var otherb in books)        {            if(otherb != b && otherb.author == b.author)            {                find = false;            }        }         if(find)        {            yield return b;        }     } } 

normally, time complexity o(books.count^2), there if(find) statement in outer loop , may change loop times.

so questions are:

1. what time complexity of method?
2. how did calculate it?

i'm waiting online answer.

thank in advance.

you go through each book in outer loop (n) , each outer book go through each otherb in inner loop (n times) the time complexity o(n^2).

the yield return not change complexity of algorithm, creates iterator pattern if traverse whole list calling function, go through iterations in algo.

what yield keyword used in c#?

to optimize algorithm, btilly mention, 2 passes on collection, on first pass store number of books per author in hash table , on second pass check if author has more 1 book using hash table (assuming constant time lookup) , yield book if does:

public list<book> shoot() {     var authors = new dictionary<string, int>();     foreach(var b in books)      {         if(authors.containskey(b.author))             authors[b.author] ++;         else             authors.add(b.author, 1);     }      foreach(var b in books)      {         if(authors[b.author] == 1)             yield return b;     } } 

this way have linear time complexity of o(n), note need o(n) space in case.