In this article, we will discuss how to implement a Stack using list in C++ STL.
Stack is a linear data structure which follows. LIFO(Last In First Out) or FILO(First In Last Out). It mainly supports 4 major operations:
1. Push: Push an element into the stack.
2. Pop: Removes the element by following the LIFO order.
3. Top: Returns the element present at the top of the stack.
4. Empty: Returns whether the stack is empty or not.
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Below is the implementation of the above approach:
C++
// C++ implementation of stack // using list STL #include <bits/stdc++.h> using namespace std;   template <typename T> // templating it so that any data type can be used   class Stack { public:     list<T> l;     int cs = 0;     // current size of the stack       // pushing an element into the stack     void push(T d)     {         cs++;         // increasing the current size of the stack         l.push_front(d);     }       // popping an element from the stack     void pop()     {         if (cs <= 0) {             // cannot pop us stack does not contain an             // elements             cout << "Stack empty" << endl;         }         else {             // decreasing the current size of the stack             cs--;             l.pop_front();         }     }       // if current size is 0 then stack is empty     bool empty() { return cs == 0; }       // getting the element present at the top of the stack     T top() { return l.front(); }     int size()     {         // getting the size of the stack         return cs;     }       // printing the elements of the stack     void print()     {         for (auto x: l) {             cout << x << endl;         }     } }; int main() {     Stack<int> s;     s.push(10); // pushing into the stack     s.push(20);     s.push(30);     s.push(40);     cout << "Current size of the stack is " << s.size()          << endl;     cout << "The top element of the stack is " << s.top()          << endl;     s.pop(); // popping from the stack     cout << "The top element after 1 pop operation is "         << s.top()          << endl; // printing the top of the stack     s.pop(); // popping     cout << "The top element after 2 pop operations is "         << s.top() << endl;     cout << "Size of the stack after 2 pop operations is "         << s.size() << endl;     return 0; } |
Output
Current size of the stack is 4 The top element of the stack is 40 The top element after 1 pop operation is 30 The top element after 2 pop operations is 20 Size of the stack after 2 pop operations is 2
Time Complexity: O(1) for both push and pop operations in the stack.
Auxiliary Space: O(N)
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