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Questions tagged [pushdown-automaton]

A pushdown automaton (PDA) is a finite-state automaton with added stack based memory. It is a mathematical description of an algorithm for parsing context-free languages.

PDAs extend finite automata via a stack-based memory, and transitions can push/pop symbols to/from the stack. Deterministic PDAs (ones for which there exists only one legal transition at any time) are strictly weaker than non-deterministic ones; such is not the case for finite automata (PDAs are more powerful) or Turing machines (PDAs are weaker).

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How to keep track of string index for Pushdown Automaton?

i have to construct this PDA, but i am confused on how is possible to keep track a string index xi and yi? thanks in advance Construct a PDA that accepts { x#y | x, y in {0, 1}* such that x ≠ y and xi = yi for some i, 1 ≤ i ≤ min(|x|, |y|)…
wildplace
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Struggling with this PDA construction

In human language: list of words (constructed from ‘a’s and ‘b’s ) separated by ‘c’s and exists at least one word in some index i that has more letters ‘a’ in it then word in index i+2
urag
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In push down automaton stack is shared with all other states?

I want to know that in push down automaton stack is shared with all other states or not?
Onkar Shinde
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CFG and PDA for the grammar that has perfectly nested parentheses and brackets

I gotta make a CFG and PDA for the grammar that has perfectly nested parentheses and brackets. S -> [S] S -> (S) S -> SS S -> Epsilon Not sure if this is correct, or how to make the PDA from it?
y2k
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PDA and CF grammar for L={w| w={a,b}* such that 2* (number of "a"-s in w) != 3* (number of "b"-s in w) +2 }

I found the following problem in a past exam: Construct a PDA with void stack acceptance and a CF grammar for the language: L={w| w={a,b}* such that 2* (number of "a"-s in w) != 3* (number of "b"-s in w) +2 } Assume that w = {a, b}* with that…
Bianca Stan
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Find the center letter in 2 pdf (2 stack) in automata

Draw a 2PDA that accepts MIDDLE A of all words that have A as the middle letter. Also, Explain the Logic of it.
Sohaib Aslam
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