Create a customized data structure which evaluates functions in O(1)

2.2

Create a customized data structure such that it has functions :-
GetLastElement();
RemoveLastElement();
AddElement()
GetMin()

All the functions should be of O(1)

Question Source : amazon interview questions

Approach :
1) create a custom stack of type structure with two elements, (element, min_till_now)
2) implement the functions on this custom data type

// program to demonstrate customized data structure
// which supports functions in O(1)
#include <iostream>
#include <vector>
using namespace std;
const int MAXX = 1000;

// class stack
class stack {
    int minn;
    int size;

public:
    stack()
    {
        minn = 99999;
        size = -1;
    }
    vector<pair<int, int> > arr;
    int GetLastElement();
    int RemoveLastElement();
    int AddElement(int element);
    int GetMin();
};

// utility function for adding a new element
int stack::AddElement(int element)
{
    if (size > MAXX) {
        cout << "stack overflow, max size reached!\n";
        return 0;
    }
    if (element < minn)
        minn = element;
    arr.push_back(make_pair(element, minn));
    size++;
    return 1;
}

// utility function for returning last element of stack
int stack::GetLastElement()
{
    if (size == -1) {
        cout << "No elements in stack\n";
        return 0;
    }
    return arr[size].first;
}

// utility function for removing last element successfully;
int stack::RemoveLastElement()
{
    if (size == -1) {
        cout << "stack empty!!!\n";
        return 0;
    }

    // updating minimum element
    if (size > 0 && arr[size - 1].second > arr[size].second) {
        minn = arr[size - 1].second;
    }
    arr.pop_back();
    size -= 1;
    return 1;
}

// utility function for returning min element till now;
int stack::GetMin()
{
    if (size == -1) {
        cout << "stack empty!!\n";
        return 0;
    }
    return arr[size].second;
}

// Driver code
int main()
{
    stack s;
    int success = s.AddElement(5);
    if (success == 1)
        cout << "5 inserted successfully\n";

    success = s.AddElement(7);
    if (success == 1)
        cout << "7 inserted successfully\n";

    success = s.AddElement(3);
    if (success == 1)
        cout << "3 inserted successfully\n";
    int min1 = s.GetMin();
    cout << "min element  :: " << min1 << endl;

    success = s.RemoveLastElement();
    if (success == 1)
        cout << "removed successfully\n";

    success = s.AddElement(2);
    if (success == 1)
        cout << "2 inserted successfully\n";

    success = s.AddElement(9);
    if (success == 1)
        cout << "9 inserted successfully\n";
    int last = s.GetLastElement();
    cout << "Last element :: " << last << endl;

    success = s.AddElement(0);
    if (success == 1)
        cout << "0 inserted successfully\n";
    min1 = s.GetMin();
    cout << "min element  :: " << min1 << endl;

    success = s.RemoveLastElement();
    if (success == 1)
        cout << "removed successfully\n";

    success = s.AddElement(11);
    if (success == 1)
        cout << "11 inserted successfully\n";
    min1 = s.GetMin();
    cout << "min element  :: " << min1 << endl;

    return 0;
}

Output:

5 inserted successfully
7 inserted successfully
3 inserted successfully
min element  :: 3
removed successfully
2 inserted successfully
9 inserted successfully
Last element :: 9
0 inserted successfully
min element  :: 0
removed successfully
11 inserted successfully
min element  :: 2

Time complexity : Each function runs in O(1)

This article is contributed by Mandeep Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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