ตารางแฮชเป็นโครงสร้างข้อมูลที่ใช้เก็บคู่คีย์-ค่า ฟังก์ชันแฮชถูกใช้โดยตารางแฮชเพื่อคำนวณดัชนีลงในอาร์เรย์ที่จะแทรกหรือค้นหาองค์ประกอบ
Double hashing เป็นเทคนิคการแก้ปัญหาการชนกันในตาราง Open Addressed Hash การแฮชแบบคู่ใช้แนวคิดในการใช้ฟังก์ชันแฮชที่สองเพื่อกำหนดคีย์เมื่อเกิดการชนกัน
นี่คือโปรแกรม C++ ที่ใช้เชื่อมโยงตารางแฮชด้วยการแฮชสองครั้ง
อัลกอริทึม
สำหรับการค้นหาคีย์:
Begin Declare Function SearchKey(int k, HashTable *ht) int hashVal= HashFunc1(k, ht->s) int stepSize= HashFunc2(k, ht->s) while (ht->t[hashVal].info != Emp and ht->t[hashVal].e != k) hashVal = hashVal + stepSize hashVal = hashVal % ht->s return hashVal End
สำหรับการแทรก:
Begin. Declare Function Insert(int k, HashTable *ht) int pos = SearchKey(k, ht) if (ht->t[pos].info != Legi ) ht->t[pos].info = Legi ht->t[pos].e = k End
สำหรับดิสเพลย์:
Begin Declare function display(HashTable *ht) for (int i = 0; i < ht->s; i++) int v= ht->t[i].e; if (!v) Print "Position: " Print the position of the pointer Print " Element: Null" else Print "Position: " Print the position of the pointer Print " Element: " Print the element End.
สำหรับฟังก์ชันแฮช:
Begin Declare function Rehash(HashTable *ht) int s = ht->s HashTableEntry *t= ht->t ht = initiateTable(2*s) for (int i = 0; i < s; i++) if (t[i].info == Legi) Insert(t[i].e, ht) free(t) return ht End.
โค้ดตัวอย่าง
#include <iostream>
#include <cstdlib>
#define T_S 5
using namespace std;
enum EntryType {Legi, Emp};
struct HashTableEntry {
int e;
enum EntryType info;
};
struct HashTable {
int s;
HashTableEntry *t;
};
int HashFunc1(int k, int s) {
return k % s;
}
int HashFunc2(int k, int s) {
return (k * s - 1) % s;
}
HashTable *initiateTable(int s) {
HashTable *ht;
if (s < T_S) {
cout<<"Table Size is Too Small"<<endl;
return NULL;
}
ht= new HashTable;
if (ht == NULL) {
cout<<"Out of Space"<<endl;
return NULL;
}
ht->s = s;
ht->t = new HashTableEntry[ht->s];
if (ht->t== NULL) {
cout<<"Table Size is Too Small"<<endl;
return NULL;
}
for (int i = 0; i < ht->s; i++) {
ht->t[i].info = Emp;
ht->t[i].e=NULL;
}
return ht;
}
int SearchKey(int k, HashTable *ht) {
int hashVal= HashFunc1(k, ht->s);
int stepSize= HashFunc2(k, ht->s);
while (ht->t[hashVal].info != Emp &&
ht->t[hashVal].e != k) {
hashVal = hashVal + stepSize;
hashVal = hashVal % ht->s;
}
return hashVal;
}
void Insert(int k, HashTable *ht) {
int pos = SearchKey(k, ht);
if (ht->t[pos].info != Legi ) {
ht->t[pos].info = Legi;
ht->t[pos].e = k;
}
}
void display(HashTable *ht) {
for (int i = 0; i < ht->s; i++) {
int v= ht->t[i].e;
if (!v)
cout<<"Position: "<<i + 1<<" Element: Null"<<endl;
else
cout<<"Position: "<<i + 1<<" Element: "<<v<<endl;
}
}
HashTable *Rehash(HashTable *ht) {
int s = ht->s;
HashTableEntry *t= ht->t;
ht = initiateTable(2*s);
for (int i = 0; i < s; i++) {
if (t[i].info == Legi)
Insert(t[i].e, ht);
}
free(t);
return ht;
}
int main() {
int v, s, pos, i = 1;
int c;
HashTable *ht;
while(1) {
cout<<"1.Initialize size of the table"<<endl;
cout<<"2.Insert element into the table"<<endl;
cout<<"3.Display Hash Table"<<endl;
cout<<"4.Rehash Hash Table"<<endl;
cout<<"5.Exit"<<endl;
cout<<"Enter your choice: ";
cin>>c;
switch(c) {
case 1:
cout<<"Enter size of the Hash Table: ";
cin>>s;
ht = initiateTable(s);
break;
case 2:
if (i > ht->s) {
cout<<"Table is Full, Rehash the table"<<endl;
continue;
}
cout<<"Enter element to be inserted: ";
cin>>v;
Insert(v, ht);
i++;
break;
case 3:
display(ht);
break;
case 4:
ht= Rehash(ht);
break;
case 5:
exit(1);
default:
cout<<"\nEnter correct option\n";
}
}
return 0;
}
ผลลัพธ์
1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 1 Enter size of the Hash Table: 4 Table Size is Too Small Enter your choice: 1 Enter size of the Hash Table: 10 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 1 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 3 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 4 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 5 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 6 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 7 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 8 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 9 Enter correct option 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 9 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 10 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 11 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Table is Full, Rehash the table 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 12 Enter correct option 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Table is Full, Rehash the table 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Table is Full, Rehash the table 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 3 Position: 1 Element: 10 Position: 2 Element: 1 Position: 3 Element: 11 Position: 4 Element: 3 Position: 5 Element: 4 Position: 6 Element: 5 Position: 7 Element: 6 Position: 8 Element: 7 Position: 9 Element: 8 Position: 10 Element: 9 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 4 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 3 Position: 1 Element: Null Position: 2 Element: 1 Position: 3 Element: Null Position: 4 Element: 3 Position: 5 Element: 4 Position: 6 Element: 5 Position: 7 Element: 6 Position: 8 Element: 7 Position: 9 Element: 8 Position: 10 Element: 9 Position: 11 Element: 10 Position: 12 Element: 11 Position: 13 Element: Null Position: 14 Element: Null Position: 15 Element: Null Position: 16 Element: Null Position: 17 Element: Null Position: 18 Element: Null Position: 19 Element: Null Position: 20 Element: Null 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 2 Enter element to be inserted: 20 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 3 Position: 1 Element: 20 Position: 2 Element: 1 Position: 3 Element: Null Position: 4 Element: 3 Position: 5 Element: 4 Position: 6 Element: 5 Position: 7 Element: 6 Position: 8 Element: 7 Position: 9 Element: 8 Position: 10 Element: 9 Position: 11 Element: 10 Position: 12 Element: 11 Position: 13 Element: Null Position: 14 Element: Null Position: 15 Element: Null Position: 16 Element: Null Position: 17 Element: Null Position: 18 Element: Null Position: 19 Element: Null Position: 20 Element: Null 1.Initialize size of the table 2.Insert element into the table 3.Display Hash Table 4.Rehash Hash Table 5.Exit Enter your choice: 5
