Struktura podataka steka i implementacija u Pythonu, Javi i C / C ++

U ovom vodiču naučit ćete o strukturi podataka steka i njihovoj implementaciji u Pythonu, Javi i C / C ++.

Stog je korisna struktura podataka u programiranju. Baš je poput hrpe tanjura držanih jedna na drugoj.

Prikaz sloga sličan hrpi tanjura

Razmislite o stvarima koje možete učiniti s takvom hrpom tanjura

  • Stavite novi tanjur na vrh
  • Uklonite gornju ploču

Ako želite ploču na dnu, prvo morate ukloniti sve ploče na vrhu. Takav se aranžman naziva Last In First Out - posljednja stavka koja je prva stavka koja izađe.

LIFO princip sloga

U programskom smislu, stavljanje stavke na vrh stoga naziva se push, a uklanjanje stavke naziva pop .

Složite push i pop operacije

Na gornjoj je slici, iako je stavka 2 zadnja zadržana, prvo uklonjena - pa slijedi načelo Last In First Out (LIFO) .

Stog možemo implementirati u bilo koji programski jezik poput C, C ++, Java, Python ili C #, ali specifikacija je gotovo ista.

Osnovne operacije steka

Stog je objekt (apstraktni tip podataka - ADT) koji omogućuje sljedeće operacije:

  • Guranje : dodajte element na vrh stoga
  • Skok : Uklonite element s vrha hrpe
  • IsEmpty : Provjerite je li stog prazan
  • IsFull : Provjerite je li stog pun
  • Zavirite : Dohvatite vrijednost gornjeg elementa bez uklanjanja

Rad strukture podataka steka

Operacije rade kako slijedi:

  1. Pokazivač zvan TOP koristi se za praćenje gornjeg elementa u stogu.
  2. Pri inicijalizaciji stoga postavljamo njegovu vrijednost na -1 kako bismo usporedbom mogli provjeriti je li stog prazan TOP == -1.
  3. Pritiskom na element povećavamo vrijednost TOP-a i postavljamo novi element u položaj na koji pokazuje TOP.
  4. Nakon iskakanja elementa, vraćamo element na koji ukazuje TOP i smanjujemo njegovu vrijednost.
  5. Prije guranja provjeravamo je li stog već pun
  6. Prije pucanja provjeravamo je li stog već prazan
Rad strukture podataka steka

Implementacije stoga u Python, Java, C i C ++

Najčešća implementacija stoga je upotreba nizova, ali se također može implementirati pomoću popisa.

Python Java C C + 
 # Stack implementation in python # Creating a stack def create_stack(): stack = () return stack # Creating an empty stack def check_empty(stack): return len(stack) == 0 # Adding items into the stack def push(stack, item): stack.append(item) print("pushed item: " + item) # Removing an element from the stack def pop(stack): if (check_empty(stack)): return "stack is empty" return stack.pop() stack = create_stack() push(stack, str(1)) push(stack, str(2)) push(stack, str(3)) push(stack, str(4)) print("popped item: " + pop(stack)) print("stack after popping an element: " + str(stack)) 
 // Stack implementation in Java class Stack ( private int arr(); private int top; private int capacity; // Creating a stack Stack(int size) ( arr = new int(size); capacity = size; top = -1; ) // Add elements into stack public void push(int x) ( if (isFull()) ( System.out.println("OverFlowProgram Terminated"); System.exit(1); ) System.out.println("Inserting " + x); arr(++top) = x; ) // Remove element from stack public int pop() ( if (isEmpty()) ( System.out.println("STACK EMPTY"); System.exit(1); ) return arr(top--); ) // Utility function to return the size of the stack public int size() ( return top + 1; ) // Check if the stack is empty public Boolean isEmpty() ( return top == -1; ) // Check if the stack is full public Boolean isFull() ( return top == capacity - 1; ) public void printStack() ( for (int i = 0; i <= top; i++) ( System.out.println(arr(i)); ) ) public static void main(String() args) ( Stack stack = new Stack(5); stack.push(1); stack.push(2); stack.push(3); stack.push(4); stack.pop(); System.out.println("After popping out"); stack.printStack(); ) )
 // Stack implementation in C #include #include #define MAX 10 int count = 0; // Creating a stack struct stack ( int items(MAX); int top; ); typedef struct stack st; void createEmptyStack(st *s) ( s->top = -1; ) // Check if the stack is full int isfull(st *s) ( if (s->top == MAX - 1) return 1; else return 0; ) // Check if the stack is empty int isempty(st *s) ( if (s->top == -1) return 1; else return 0; ) // Add elements into stack void push(st *s, int newitem) ( if (isfull(s)) ( printf("STACK FULL"); ) else ( s->top++; s->items(s->top) = newitem; ) count++; ) // Remove element from stack void pop(st *s) ( if (isempty(s)) ( printf(" STACK EMPTY "); ) else ( printf("Item popped= %d", s->items(s->top)); s->top--; ) count--; printf(""); ) // Print elements of stack void printStack(st *s) ( printf("Stack: "); for (int i = 0; i items(i)); ) printf(""); ) // Driver code int main() ( int ch; st *s = (st *)malloc(sizeof(st)); createEmptyStack(s); push(s, 1); push(s, 2); push(s, 3); push(s, 4); printStack(s); pop(s); printf("After popping out"); printStack(s); )
 // Stack implementation in C++ #include #include using namespace std; #define MAX 10 int size = 0; // Creating a stack struct stack ( int items(MAX); int top; ); typedef struct stack st; void createEmptyStack(st *s) ( s->top = -1; ) // Check if the stack is full int isfull(st *s) ( if (s->top == MAX - 1) return 1; else return 0; ) // Check if the stack is empty int isempty(st *s) ( if (s->top == -1) return 1; else return 0; ) // Add elements into stack void push(st *s, int newitem) ( if (isfull(s)) ( printf("STACK FULL"); ) else ( s->top++; s->items(s->top) = newitem; ) size++; ) // Remove element from stack void pop(st *s) ( if (isempty(s)) ( printf(" STACK EMPTY "); ) else ( printf("Item popped= %d", s->items(s->top)); s->top--; ) size--; cout << endl; ) // Print elements of stack void printStack(st *s) ( printf("Stack: "); for (int i = 0; i < size; i++) ( cout

Stack Time Complexity

For the array-based implementation of a stack, the push and pop operations take constant time, i.e. O(1).

Applications of Stack Data Structure

Although stack is a simple data structure to implement, it is very powerful. The most common uses of a stack are:

  • To reverse a word - Put all the letters in a stack and pop them out. Because of the LIFO order of stack, you will get the letters in reverse order.
  • In compilers - Compilers use the stack to calculate the value of expressions like 2 + 4 / 5 * (7 - 9) by converting the expression to prefix or postfix form.
  • In browsers - The back button in a browser saves all the URLs you have visited previously in a stack. Each time you visit a new page, it is added on top of the stack. When you press the back button, the current URL is removed from the stack, and the previous URL is accessed.

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