cpp pgm to implement stack in O(1) time complexity

Author: n0r01tk

15-Stack/Stack_Implementaion_O-1_time_complexity.cpp

@@ -0,0 +1,133 @@
+#include <iostream> 
+#include <stdlib.h> 
+  
+using namespace std; 
+  
+/* A simple stack class with  
+basic stack funtionalities */
+class Stack { 
+private: 
+    static const int max = 100; 
+    int arr[max]; 
+    int top; 
+  
+public: 
+    Stack() { top = -1; } 
+    bool isEmpty(); 
+    bool isFull(); 
+    int pop(); 
+    void push(int x); 
+}; 
+  
+/* Stack's member method to check  
+if the stack is iempty */
+bool Stack::isEmpty() 
+{ 
+    if (top == -1) 
+        return true; 
+    return false; 
+} 
+  
+/* Stack's member method to check  
+if the stack is full */
+bool Stack::isFull() 
+{ 
+    if (top == max - 1) 
+        return true; 
+    return false; 
+} 
+  
+/* Stack's member method to remove  
+an element from it */
+int Stack::pop() 
+{ 
+    if (isEmpty()) { 
+        cout << "Stack Underflow"; 
+        abort(); 
+    } 
+    int x = arr[top]; 
+    top--; 
+    return x; 
+} 
+  
+/* Stack's member method to insert  
+an element to it */
+void Stack::push(int x) 
+{ 
+    if (isFull()) { 
+        cout << "Stack Overflow"; 
+        abort(); 
+    } 
+    top++; 
+    arr[top] = x; 
+} 
+  
+/* A class that supports all the stack  
+operations and one additional 
+  operation getMin() that returns the  
+minimum element from stack at 
+  any time.  This class inherits from  
+the stack class and uses an 
+  auxiliarry stack that holds minimum  
+elements */
+class SpecialStack : public Stack { 
+    Stack min; 
+  
+public: 
+    int pop(); 
+    void push(int x); 
+    int getMin(); 
+}; 
+  
+/* SpecialStack's member method to insert 
+ an element to it. This method 
+   makes sure that the min stack is also  
+updated with appropriate minimum 
+   values */
+void SpecialStack::push(int x) 
+{ 
+    if (isEmpty() == true) { 
+        Stack::push(x); 
+        min.push(x); 
+    } 
+    else { 
+        Stack::push(x); 
+        int y = min.pop(); 
+        min.push(y); 
+        if (x < y) 
+            min.push(x); 
+        else
+            min.push(y); 
+    } 
+} 
+  
+/* SpecialStack's member method to  
+remove an element from it. This method 
+   removes top element from min stack also. */
+int SpecialStack::pop() 
+{ 
+    int x = Stack::pop(); 
+    min.pop(); 
+    return x; 
+} 
+  
+/* SpecialStack's member method to get 
+ minimum element from it. */
+int SpecialStack::getMin() 
+{ 
+    int x = min.pop(); 
+    min.push(x); 
+    return x; 
+} 
+  
+int main() 
+{ 
+    SpecialStack s; 
+    s.push(10); 
+    s.push(20); 
+    s.push(30); 
+    cout << s.getMin() << endl; 
+    s.push(5); 
+    cout << s.getMin(); 
+    return 0; 
+}