c++ hashing 3413, 3869, 1897, 3346, 4325, 1657, 1, 2199, 1411, 874, 4323, 2759,

Question

c++ hashing

3413, 3869, 1897, 3346, 4325, 1657, 1, 2199, 1411, 874, 4323, 2759, 2457, 4071, 1236, 2156, 1610, 4538, 2161, 4632 Given the above set of numbers, choose an array size for a hash array (aka table) (Note: empirically speaking, we find we get the best results when a hash array is approximately half full). Think of two different possible hashing functions you could use with this set of numbers to hash the numbers into indices in the hash array (Note: for this particular assignment, I ask that you not use google, or, at least, don't use hashing functions you find when you google. Please come up with 2 different possible hashing functions on your own. Extra points will be given to the most creative yet easy to calculate functions). Show a hash array for three hashing functions: your two hashing functions and the hashing function given in class as such: Let c =(sqrt(5) -1)/2 h(k) = floor(m * ((k*c) - floor(k*c))) Where k is the key, and m is 7 You will have to mod the different functions by the length you chose for your array in part A Collisions will be handled as follows: the numbers will be hashed and inserted into the array in the order specified above. If a number hashes to an index that already contains a value, the new key overwrites the value. Keep track of the number of collisions for each of the three functions. Which hashing function had the fewest collisions? Which had the most? If you haven't already, implement at least one of your hashing functions as code, including a function that prints out the hash array after all keys have been inserted.

Explanation / Answer

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
const int TABLE_SIZE = 5;

/*
* HashNode Class Declaration
*/
class HashNode
{
public:
int key;
int value;
HashNode(int key, int value)
{
this->key = key;
this->value = value;
}
};

/*
* DeletedNode Class Declaration
*/
class DeletedNode:public HashNode
{
private:
static DeletedNode *entry;
DeletedNode():HashNode(-1, -1)
{}
public:
static DeletedNode *getNode()
{
if (entry == NULL)
entry = new DeletedNode();
return entry;
}
};
DeletedNode *DeletedNode::entry = NULL;
/*
* HashMap Class Declaration
*/
class HashMap
{
private:
HashNode **htable;
public:
HashMap()
{
htable = new HashNode* [TABLE_SIZE];
for (int i = 0; i < TABLE_SIZE; i++)
{
htable[i] = NULL;
}
}

~HashMap()
{
for (int i = 0; i < TABLE_SIZE; i++)
{
if (htable[i] != NULL && htable[i] != DeletedNode::getNode())
delete htable[i];
}
delete[] htable;
}
/*
* Hash Function
*/
int HashFunc(int key)
{
return key % TABLE_SIZE;
}
/*
* Insert Element at a key
*/
void Insert(int key, int value)
{
int hash_val = HashFunc(key);
int init = -1;
int deletedindex = -1;
while (hash_val != init && (htable[hash_val]
== DeletedNode::getNode() || htable[hash_val]
!= NULL && htable[hash_val]->key != key))
{
if (init == -1)
init = hash_val;
if (htable[hash_val] == DeletedNode::getNode())
deletedindex = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (htable[hash_val] == NULL || hash_val == init)
{
if(deletedindex != -1)
htable[deletedindex] = new HashNode(key, value);
else
htable[hash_val] = new HashNode(key, value);
}
if(init != hash_val)
{
if (htable[hash_val] != DeletedNode::getNode())
{
if (htable[hash_val] != NULL)
{
if (htable[hash_val]->key == key)
htable[hash_val]->value = value;
}
}
else
htable[hash_val] = new HashNode(key, value);
}
}
/*
* Search Element at a key
*/
int Search(int key)
{
int hash_val = HashFunc(key);
int init = -1;
while (hash_val != init && (htable[hash_val]
== DeletedNode::getNode() || htable[hash_val]
!= NULL && htable[hash_val]->key != key))
{
if (init == -1)
init = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (htable[hash_val] == NULL || hash_val == init)
return -1;
else
return htable[hash_val]->value;
}
/*
* Remove Element at a key
*/
void Remove(int key)
{
int hash_val = HashFunc(key);
int init = -1;
while (hash_val != init && (htable[hash_val]
== DeletedNode::getNode() || htable[hash_val]
!= NULL && htable[hash_val]->key != key))
{
if (init == -1)
init = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (hash_val != init && htable[hash_val] != NULL)
{
delete htable[hash_val];
htable[hash_val] = DeletedNode::getNode();
}
}
};

/*
* Main Contains Menu
*/
int main()
{
HashMap hash;
int key, value;
int choice;
while(1)
{
cout<<" ----------------------"<<endl;
cout<<"Operations on Hash Table"<<endl;
cout<<" ----------------------"<<endl;
cout<<"1.Insert element into the table"<<endl;
cout<<"2.Search element from the key"<<endl;
cout<<"3.Delete element at a key"<<endl;
cout<<"4.Exit"<<endl;
cout<<"Enter your choice: ";
cin>>choice;
switch(choice)
{
case 1:
cout<<"Enter element to be inserted: ";
cin>>value;
cout<<"Enter key at which element to be inserted: ";
cin>>key;
hash.Insert(key, value);
break;
case 2:
cout<<"Enter key of the element to be searched: ";
cin>>key;
if(hash.Search(key) == -1)
{
cout<<"No element found at key "<<key<<endl;
continue;
}
else
{
cout<<"Element at key "<<key<<" : ";
cout<<hash.Search(key)<<endl;
}
break;
case 3:
cout<<"Enter key of the element to be deleted: ";
cin>>key;
hash.Remove(key);
break;
case 4:
exit(1);
default:
cout<<" Enter correct option ";
}
}
return 0;
}

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