# What are the complexity guarantees of the standard containers?

Apparently ;-) the standard containers provide some form of guarantees.

What type of guarantees and what exactly are the differences between the different types of container?

Working from the SGI page (about STL) I have come up with this:

Container Types: ================ Container: Forward Container Reverse Container Random Access Container Sequence Front Insert Sequence Back Insert Sequence Associative Container Simple Associative Container Pair Associative Container Sorted Associative Container Multiple Associative Container Container Types mapped to Standard Containers ============================================= std::vector: Sequence Back Sequence Forward/Reverse/Random Container std::deque: Sequence Front/Back Sequence Forward/Reverse/Random Container std::list: Sequence Front/Back Sequence Forward/Reverse Container std::set: Sorted/Simple/Unique Associative Container Forward Container std::map: Sorted/Pair/Unique Associative Container Forward Container std::multiset: Sorted/Simple/Multiple Associative Container Forward Container std::multimap: Sorted/Pair/Multiple Associative Container Forward Container Container Guarantees: ===================== Simp or For Rev Rand Front Back Assoc Sort Mult Cont: Cont: Cont Cont: Sequ: Sequ: Sequ: Cont: Cont: Cont: Copy Const: O(n) Fill Const: O(n) begin() O(1) end() O(1) rbegin() O(1) rend() O(1) front() O(1) push_front() O(1) pop_front() O(1) push_back() O(1) pop_back() O(1) Insert() O(ln(n)) Insert: fill O(n) Insert: range O(n) O(kln(n)+n) size() O(n) swap() O(1) erase key O(ln(n)) erase element O(1) erase range O(ln(n)+S) count() O(log(n)+k) find() O(ln(n)) equal range O(ln(n)) Lower Bound/Upper Bound O(ln(n)) Equality O(n) InEquality O(n) Element Access O(1)

## Answers

I found the nice resource *Standard C++ Containers*. Probably this is what you all looking for.

**VECTOR**

**Constructors**

vector<T> v; Make an empty vector. O(1) vector<T> v(n); Make a vector with N elements. O(n) vector<T> v(n, value); Make a vector with N elements, initialized to value. O(n) vector<T> v(begin, end); Make a vector and copy the elements from begin to end. O(n)

**Accessors**

v[i] Return (or set) the I'th element. O(1) v.at(i) Return (or set) the I'th element, with bounds checking. O(1) v.size() Return current number of elements. O(1) v.empty() Return true if vector is empty. O(1) v.begin() Return random access iterator to start. O(1) v.end() Return random access iterator to end. O(1) v.front() Return the first element. O(1) v.back() Return the last element. O(1) v.capacity() Return maximum number of elements. O(1)

**Modifiers**

v.push_back(value) Add value to end. O(1) (amortized) v.insert(iterator, value) Insert value at the position indexed by iterator. O(n) v.pop_back() Remove value from end. O(1) v.assign(begin, end) Clear the container and copy in the elements from begin to end. O(n) v.erase(iterator) Erase value indexed by iterator. O(n) v.erase(begin, end) Erase the elements from begin to end. O(n)

For other containers, refer to the page.

I'm not aware of anything like a single table that lets you compare all of them in at one glance (I'm not sure such a table would even be feasible).

Of course the ISO standard document enumerates the complexity requirements in detail, sometimes in various rather readable tables, other times in less readable bullet points for each specific method.

Also the STL library reference at http://www.cplusplus.com/reference/stl/ provides the complexity requirements where appropriate.