Question

I need the code for those contracts

Answer 1

#include<bits/stdc++.h>
using namespace std;

// class to represent the required data structure
class myStructure
{
// A resizable array
vector <int> arr;

// A hash where keys are array elements and vlaues are
// indexes in arr[]
map <int, int> Map;

public:
// A Theta(1) function to add an element to MyDS
// data structure
void add(int x)
{
// If ekement is already present, then noting to do
if(Map.find(x) != Map.end())
return;

// Else put element at the end of arr[]
int index = arr.size();
arr.push_back(x);

// and hashmap also
Map.insert(std::pair<int,int>(x, index));
}

// function to remove a number to DS in O(1)
void remove(int x)
{
// element not found then return
if(Map.find(x) == Map.end())
return;

// remove element from map
int index = Map.at(x);
Map.erase(x);

// swap with last element in arr
// then remove element at back
int last = arr.size() - 1;
swap(arr[index], arr[last]);
arr.pop_back();

// Update hash table for new index of last element
Map.at(arr[index]) = index;
}

// Returns index of element if element is present, otherwise null
int search(int x)
{
if(Map.find(x) != Map.end())
return Map.at(x);
return -1;
}

// Returns a random element from myStructure
int getRandom()
{
// Find a random index from 0 to size - 1
srand (time(NULL));
int random_index = rand() % arr.size();

// Return element at randomly picked index
return arr.at(random_index);
}   
};

// Driver main
int main()
{
myStructure ds;
ds.add(10);
ds.add(20);
ds.add(30);
ds.add(40);
cout << ds.search(30) << endl;
ds.remove(20);
ds.add(50);
cout << ds.search(50) << endl;
cout << ds.getRandom() << endl;
}