swapandpop

Swap and pop is a technique for removing an element from a dynamic array or vector without preserving order. It achieves constant-time removal by placing the last element in the position of the element being removed and then reducing the container size by one. It is commonly used in performance-critical code such as game development, particle systems, and resource pools where frequent deletions occur and maintaining strict order is not required.

To remove the element at index i in an array A of length n: if i is not the last index, set A[i] = A[n-1]; then decrease the logical size of the array by one. If i is the last element, simply decrease the size. If removal is by value rather than by index, first locate the index of the value, then apply the same steps.

Time complexity is O(1) for removal by index, and O(n) to locate by value; space usage is O(1) extra. This method does not preserve the relative order of elements, so any external references or invariants depending on order must be addressed.

In practice, swap and pop works well in languages and environments where element movement is inexpensive and where the container can be compacted by shrinking its size. If preserving order is required, alternatives such as shifting subsequent elements or using a different data structure should be considered. Some implementations expose a swap-and-pop interface as part of the array or vector utilities, making the operation easy to apply without additional bookkeeping.