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Similarly to a stack of plates, adding or removing is only practical at the top. Simple representation of a stack runtime with push and pop operations.. In computer science, a stack is an abstract data type that serves as a collection of elements with two main operations:
An abstract stack is a last-in-first-out structure, It is generally defined by three key operations: push, that inserts a data item onto the stack; pop, that removes a data item from it; and peek or top, that accesses a data item on top of the stack without removal.
The name "peek" is similar to the basic "push" and "pop" operations on a stack, but the name for this operation varies depending on data type and language. Peek is generally considered an inessential operation, compared with the more basic operations of adding and removing data, and as such is not included in the basic definition of these data ...
The stack is often used to store variables of fixed length local to the currently active functions. Programmers may further choose to explicitly use the stack to store local data of variable length. If a region of memory lies on the thread's stack, that memory is said to have been allocated on the stack, i.e. stack-based memory allocation (SBMA).
With a stack stored completely in RAM, this does implicit writes and reads of the in-memory stack: Load X, push to memory; Load 1, push to memory; Pop 2 values from memory, add, and push result to memory; for a total of 5 data cache references. The next step up from this is a stack machine or interpreter with a single top-of-stack register.
In each step, it chooses a transition by indexing a table by input symbol, current state, and the symbol at the top of the stack. A pushdown automaton can also manipulate the stack, as part of performing a transition. The manipulation can be to push a particular symbol to the top of the stack, or to pop off the top of the stack.
Stack-based algorithms manipulate data by popping data from and pushing data to the stack. Operators govern how the stack manipulates data. To emphasize the effect of a statement, a comment is often used showing the top of the stack before and after the statement; this is known as the stack effect diagram.
Push - add a single element on top of the stack, enlarging the stack by 1. Pop(k) - remove k elements from the top of the stack, where k is no more than the current stack size; Pop(k) requires O(k) time, but we wish to show that all operations take O(1) amortized time. This structure may be analyzed using the potential function: Φ = number-of ...