# Implementing own Hash Table with Open Addressing Linear Probing in C++

A hash table is a data structure which is used to store key-value pairs. Hash function is used by hash table to compute an index into an array in which an element will be inserted or searched.

Linear probing is a collision resolving technique in Open Addressed Hash tables. In this method, each cell of a hash table stores a single key–value pair. If a collision is occurred by mapping a new key to a cell of the hash table that is already occupied by another key. This method searches the table for the following closest free location and inserts the new key there.

This is a C++ Program to Implement Hash Tables with Linear Probing.

## Algorithm

Begin
Declare function Insert(int k, int v)
Declare hash_val, init, delindex to the integer pointer.
initialize hash_val = HashFunc(k)
intialize init = -1
intialize delindex = -1
while (hash_val != init and (ht[hash_val]
== DelNode::getNode() or ht[hash_val]
!= NULL and ht[hash_val]->k != k))
if (init == -1)
init = hash_val
if (ht[hash_val] == DelNode::getNode())
delindex = hash_val
hash_val = HashFunc(hash_val + 1)
if (ht[hash_val] == NULL or hash_val == init)
if(delindex != -1)
ht[delindex] = new HashTable(k, v)
else
ht[hash_val] = new HashTable(k, v)
if(init != hash_val)
if (ht[hash_val] != DelNode::getNode())
if (ht[hash_val] != NULL)
if (ht[hash_val]->k== k)
ht[hash_val]->v = v
else
ht[hash_val] = new HashTable(k, v)
End.

For search a key value:

Begin
Declare Function SearchKey(int k)
Declare hash_val, init of the integer datatype.
initialize hash_val = HashFunc(k)
intialize init = -1
while (hash_val != init and (ht[hash_val]
== DelNode::getNode() or ht[hash_val]
!= NULL and ht[hash_val]->k!= k
if (init == -1)
init = hash_val
hash_val = HashFunc(hash_val + 1)
if (ht[hash_val] == NULL or hash_val == init)
return -1
else
return ht[hash_val]->v
End.

For delete:

Begin
Declare Function Remove(int k)
Declare hash_val, init of the integer datatype.
initialize hash_val = HashFunc(k)
initialize init = -1
while (hash_val != init and (ht[hash_val]
== DelNode::getNode() or ht[hash_val]
!= NULL and ht[hash_val]->k!= k))
if (init == -1)
init = hash_val
hash_val = HashFunc(hash_val + 1)
if (hash_val != init and ht[hash_val] != NULL)
delete ht[hash_val]
ht[hash_val] = DelNode::getNode()
End.

## Example Code

Live Demo

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
const int T_S = 5;
class HashTable {
public:
int k;
int v;
HashTable(int k, int v) {
this->k = k;
this->v = v;
}
};
class DelNode:public HashTable {
private:
static DelNode *en;
DelNode():HashTable(-1, -1) {}
public:
static DelNode *getNode() {
if (en == NULL)
en = new DelNode();
return en;
}
};
DelNode *DelNode::en = NULL;
class HashMapTable {
private:
HashTable **ht;
public:
HashMapTable() {
ht = new HashTable* [T_S];
for (int i = 0; i < T_S; i++) {
ht[i] = NULL;
}
}
int HashFunc(int k) {
return k % T_S;
}
void Insert(int k, int v) {
int hash_val = HashFunc(k);
int init = -1;
int delindex = -1;
while (hash_val != init && (ht[hash_val] == DelNode::getNode() || ht[hash_val] != NULL && ht[hash_val]->k != k)) {
if (init == -1)
init = hash_val;
if (ht[hash_val] == DelNode::getNode())
delindex = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (ht[hash_val] == NULL || hash_val == init) {
if(delindex != -1)
ht[delindex] = new HashTable(k, v);
else
ht[hash_val] = new HashTable(k, v);
}
if(init != hash_val) {
if (ht[hash_val] != DelNode::getNode()) {
if (ht[hash_val] != NULL) {
if (ht[hash_val]->k== k)
ht[hash_val]->v = v;
}
} else
ht[hash_val] = new HashTable(k, v);
}
}
int SearchKey(int k) {
int hash_val = HashFunc(k);
int init = -1;
while (hash_val != init && (ht[hash_val] == DelNode::getNode() || ht[hash_val] != NULL && ht[hash_val]->k!= k)) {
if (init == -1)
init = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (ht[hash_val] == NULL || hash_val == init)
return -1;
else
return ht[hash_val]->v;
}
void Remove(int k) {
int hash_val = HashFunc(k);
int init = -1;
while (hash_val != init && (ht[hash_val] == DelNode::getNode() || ht[hash_val] != NULL && ht[hash_val]->k!= k)) {
if (init == -1)
init = hash_val;
hash_val = HashFunc(hash_val + 1);
}
if (hash_val != init && ht[hash_val] != NULL) {
delete ht[hash_val];
ht[hash_val] = DelNode::getNode();
}
}
~HashMapTable() {
delete[] ht;
}
};
int main() {
HashMapTable hash;
int k, v;
int c;
while(1) {
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;
cin>>c;
switch(c) {
case 1:
cout<<"Enter element to be inserted: ";
cin>>v;
cout<<"Enter key at which element to be inserted: ";
cin>>k;
hash.Insert(k, v);
break;
case 2:
cout<<"Enter key of the element to be searched: ";
cin>>k;
if(hash.SearchKey(k) == -1) {
cout<<"No element found at key "<<k<<endl;
continue;
} else {
cout<<"Element at key "<<k<<" : ";
cout<<hash.SearchKey(k)<<endl;
}
break;
case 3:
cout<<"Enter key of the element to be deleted: ";
cin>>k;
hash.Remove(k);
break;
case 4:
exit(1);
default:
cout<<"\nEnter correct option\n";
}
}
return 0;
}

## Output

1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter element to be inserted: 10
Enter key at which element to be inserted: 2
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter element to be inserted: 7
Enter key at which element to be inserted: 6
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter element to be inserted: 4
Enter key at which element to be inserted: 5
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter element to be inserted: 12
Enter key at which element to be inserted: 3
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter correct option
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter element to be inserted: 15
Enter key at which element to be inserted: 8
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter key of the element to be searched: 6
Element at key 6 : 7
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter key of the element to be deleted: 2
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 4