Big-O运行时，以确定List是否包含X和F（X）

Question

I am trying to understand what the Big O would be for the following method.

    for(Integer i : list){
        if(list.contains(-i))
            //doSomething
    }

I know that the contains method is O(n) and that a for loop like that is O(n) as well. Does that make the total for this method O(n * n)?

Answer 1

假设List.contains是O（n），那么是的，整个算法是O（n ^ 2）。

Answer 2

BUt if you use an iterator on your list, and use the hasNext method, then your total worst case running time will big O(n). Aprroximate formula will be a constant plus n, where n is the if condition. the iterator takes a constant time to return an object, unlike the for loop.

Answer 3

因此，假设m和n是两个列表，则总运行时间将为n + 1m + 2m + ... +（n-n + 1）m。