What is vector?

Vector is a dynamic arrary in C++ STL. It allows us to find an element with O(1), append or remove last element average complexity is O(1) and delete random element with O(N).

How

Vector uses a technique named Double Array. * If my array is not full, we add new element at end of array. * If my array is full: + Allocate an new memory = 2 * Length of current array + Copy current array to new array. + Append new element to new array.