Questions tagged [stacks]
A stack is a Last In First Out (LIFO) data structure. A common use of stacks is to store subroutine arguments and return addresses.
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Design a Pushdown automaton for $L = \{a^nb^m | n \le m \le 3n \} $
$L = \{a^nb^m | n \le m \le 3n \} $
This is by far the hardest pushdown automaton I had to design. I literally have no idea where to start. Here's my thought process. Firstly, I thought that for each ...
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Question about stack permutations
I encountered an exercise in which I am struggling to understand the solution provided even though I spent a lot of time trying to figure it out.
The exercise is the following and was taken from the ...
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What loop invariant can be used for this loop? (Algorithm to check if a sequence is stack permutable)
I've written a function that gets a permutation and checks if that permutation can be reached using a stack from an input sequence which is <1,2,3,...,n>. (we take elements from left)
For ...
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Check if a string can be obtained by a sequences of insertion of "abc"
Let $a$ initially be an empty string. One can transform $a$ into $b$ in the following way: $a$ becomes $a_{left}+$"$abc$"$+a_{right}$, where $a=a_{left}+a_{right}$ in a prior state. $a_{left}...
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Array vs Linked List Implementation of Stacks (in JS)
Let's say I want to make a Stack class in JavaScript. The class will have a push() and a pop() method. I have two options for ...
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Are arrays “more abstract” than stacks or queues?
It seems to me that an array can be used as a stack or a queue and for various other things.
In my mind this makes an array a higher order abstraction compared to those other two.
Is this an ...
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Why Prefer Two Stacks to an Array for Undo/Redo?
It seems to be a popular opinion that "the right way" to implement undo/redo is "using a stack." (particularly in the context of an algorithms and data structures interview.)
Here'...
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What is the meaning of the statement "a sequence of n PUSH, POP and MULTIPOP opreations"
I am reading CLRS 3rd Ed, chapter 17.1 (Aggregate analysis pg453) and I came across this statement.
Let us analyze a sequence of n PUSH, POP, and MULTIPOP operations on an initially
empty stack.
I ...
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Array Doubling Size Strategies
I would like to discuss resizing strategies for arrays please. If you have an array of $k$ initial size and it gets full, so you would like to choose from one of the following approaches:
Approach 1: ...
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Are recursion and a stack equivalent in terms of inplementing DFS?
It is well known that DFS can be implemented either with recursion or a stack, and that both approaches are equivalent, but how far can we take that statement? Consider the following LeetCode problem:
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Iterative version of depth-first-search code to detect cycle in a directed graph [duplicate]
I have solved a problem that required me to find if the given directed graph had a cycle or not. The deal is, I used a recursive approach to solve it in the depth-first-search method. I was just ...
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`STACK-FULL` and `QUEUE-FULL` with worst-case $\Theta(1)$
There are two problems in CLRS about implementing stacks and queues with singly linked lists. I know the solutions, I know how STACK-EMPTY and ...
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How to sort a queue using a temporary stack?
Suppose we have N natural numbers in a queue. ex queue = [3, 14, 1, 20] and an empty stack
We are allowed to make only two actions:
Action "x": Dequeue an element from the queue and push it ...
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Why is the stack smaller than the heap?
From what I understand, stack and heap grow in opposite directions:
However, why is it then the case that the stack is sometimes statically allocated, and generally smaller than the heap?
We hear ...
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Using saved registers at the main function with no other function calls [RISC-V]
The convention when a function is going to use a saved register is to save the contents of that register to the stack in case the caller (if there's one? the main function doesn't have one) had been ...
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Stack without duplicates
I was thinking about the implementation of a DFS on graphs, and particularly about space complexity. The DFS algorithm can be implemented with a stack data structure. When a vertex $v$ is met during ...
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purpose of stack segment in assembly language
The code snippet below is the "beginning lines of an assembly language program" used to display a single line string .
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Implement Immediate Smaller Element problem using Stack
Immediate Smaller Element Problem:
Given an integer array arr of size $n$. For each element in the array, check whether the right adjacent element (on the next ...
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Why divide a stack into two parts and store them separately in main-memory and hard-drive a bad idea?
I'm learning data structure and trying to solve problem related to Computer Game like Chess/Go. There is a line in my book on the section of DFS algorithm, which is implemented by two stacks: one for ...
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write adt for stack operations
Ok, I dont understand whats the difference between:
write code for stack operations and write adt for stack operations?
lets say the operation is push() and pop(). So what different code is to be ...
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Black-Box Machine
Suppose we have mysterious machine which return median $m$ of given set $S$ and set $S/\{m\}$ in constant time, where $S/\{m\}$ denotes the difference of $S$ and element $m$. Prove that we can sort ...
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How to draw the heap for an array in Java?
I have an assignment to draw the heap after an ArrayList and a LinkedList is created.
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How to convert a recursive function to a non recursive one using stack while keeping memoization?
Let's say I want to count the number of ways a string can be decoded, once encoding algorithm follows this map: 'a'=>'1', 'b'=>'2', ... 'z'=>'26'.
I could ...
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How does the OS handle multiple stacks in its physical memory?
Without assuming ASLR...
Processes have virtual addresses, and they manage stacks & heaps of their own. However, these all get mapped to physical addresses somewhere on the memory.
Let's say we ...
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Automatic stack
Each context-free language has an automatic stack received by a non-deterministic blank.
That is, it will not uphold the following determinism requirement:
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Call stack is hard to maintain in my brain. What should I?
When I study Binary Search Tree, I try to use a pencil and paper to scratch the process of in-order traversal. However, I find that it is hard to maintain the call stack in my brain without paper and ...
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Is there a known way to make an efficient, compact, and fully persistent stack or queue?
In the world of mutable/ephemeral data structures and imperative programming languages, one of the classic ways to implement a stack or queue is to use array doubling: use mutation to fill up or empty ...
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Same computation order using postfix notation?
I'm trying to understand arithmetic using stacks. Specifically converting infix notation to postfix notation. My question is how you convert an expression like: 1 + (2 + 3) + (4 + 5)
that computes in ...
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Formal definition of a language accepted by PDA
I am a bit confused on how to give a formal definition of the language accepted by A?
I can describe it by "The language of all strings starting with n-many a's or n-many c's followed by n-many b's" ...
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Implementing an efficent priority queue using only stacks
Is it possible to implement an efficient priority queue (as efficient as a heap) only using the stack data structure?
The usual efficiency for a priority queue which is implemented using a heap is :
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Why are primitive types stored in a stack in systems level software?
Firstly 2 disclaimers, I am very new to the concept of a stack at a low level. I've only encountered it because I'm learning rust and the docs mention it. Secondly, I am aware of another similar ...
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Why do we do topological sorting to find shortest or longest path in weighted DAG?
I was wondering why do we need to do the topological sort before performing relaxing of edges.
Wouldn't it'd be better if we do :
if starting vertex is "s"
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Why postfix is used more often than prefix expression?
i was reading stack and i came across the infix, preifx and postfix expression.So i understood that why postfix /prefix expressions are preferred over infix expression ( due to its unambiguous nature) ...
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Priority Queue Using Stack
Can one build a priority queue using stacks, such that the priority queue has the same complexity for each operation.
Could it be done? If so how? If not what is the best solution that can be done?
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When does kernel accessing virtual memory cause problems
I'm working with the CPU Pintos and have a question that is:
In which situations can the kernel accessing the data in virtual memory via a pointer lead to problems? And how do you avoid them?
I know ...
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Is call stack compile time or runtime detail?
I'm sorry if the question is quite naive, but I don't understand if a call stack is a language implementation detail or it depends on OS?
What I'm trying to understand is what decides how to store ...
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Stack Permutation Algorithm
I was recently designing a Forth stack machine. I have an atomic instruction which rotates the top N elements.
For example if the top of the stack is on the left, then say the N=3 rotate instruction ...
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Can a programming language be designed to use a fixed amount of memory?
I have been toying around with the idea of creating a programming language as a side-project, specifically trying to get extreme performance out of a machine.
I have been thinking about the ...
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Implement heap using stack data structure
I want to implement a heap using the stack data structure. I have searched a lot on the internet. But I do not get any clue how to implement it.
Can you please help me to implement a heap using the ...
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Minimum descending stacks
Assume a randomly ruffled pack of n cards with numbers from 1 to n. Each time we pick the top card from the pack (while there are still cards) and we put them according to the following rules:
The ...
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Manage event programming under a stack-oriented language
I wonder how events, or more broadly reactive programming, could be managed in a simple stack-oriented language.
For example, let's imagine a context where there is a button that displays a small ...
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Is it theoretically possible to dynamically grow array size in stack memory?
I was wondering, given the usual stack memory functioning, whether it is possible for an array like primitive type allowed to grow in size to exist.
The functioning of such primitive type is as ...
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Generate all permutations of 1 to n with i stacks
Assume we have i stacks. the possible actions are:
push to first stack form input
pop from stack i and push it to stack i+1
pop from last stack to output
If we have numbers of 1 to n starting from 1 ...
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Formal semantics of a mutable/imperative stack
When introducing formal semantics for data structures, immutable stacks are a nice simple example :
$\mathit{is\_empty}(\mathit{create()})=\mathrm{True}$
$\mathit{is\_empty}(\mathit{push}(e, s))=\...
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Implementing a symbol table with a hash table and a stack
I was in class today, in a Language Translations course, thinking about the best way to write a symbol table for a compiler. My professor showed us a hash-table with linked-lists connecting different ...
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Multiple post-fix expressions for an in-fix expression
Today I was learning to convert post-fix expressions to in-fix expressions and vice versa. What I want to know is whether a post-fix expression can have more than one infix representations.
For ...
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kPDA handling multiple epsilon transtions
I'm assigned to build a kPDA with 2 stacks that handles {w#w, where w is a string of (0,1)*}. I understand the # delineates the two strings, but I'm unsure of the logic when popping off stacks with ...
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Amortized time complexity for double stack emulated queue
Assume that we have a data type $stack$ which has two operation $push$ and $pop$, both operations' time complexity is $O(1)$ in worst case. The $stack$ also has a property $size$ indicate how many ...
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Binary trees and preallocated nodes
I want to design a binary tree with preallocated nodes, in order to avoid calling malloc/free every time I want to insert/delete a node. The problem is I don't know ahead of time how many nodes the ...
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