Question

C++ question:

Using a standard dictionary, and a table size that approximates a load factor of 1,
compare the number of collisions produced by the hash function in Figure 5.4 and
the hash function in Figure 5.55. (Please program in C++ with explanations)

/** Figure 5.4
* A hash routine for string objects.
*/
unsigned int hash( const string & key, int tableSize )
{
unsigned int hashVal = 0;

for( char ch : key )
hashVal = 37 * hashVal + ch;

return hashVal % tableSize;
}

/** Figure 5.55
* FNV-1a hash routine for string objects.
*/
unsigned int hash( const string & key, int tableSize )
{
unsigned int hashVal = 2166136261;

for( char ch : key )
hashVal = ( hashVal ˆ ch )* 16777619;

return hashVal % tableSize;
}

Answer 1

1. #include<iostream>

2. #include<cstdlib>

3. #include<string>

4. #include<cstdio>

5. using namespace std;

6. const int TABLE_SIZE = 128;

8. /*

9.  * HashEntry Class Declaration

10.  */

11. class HashEntry

12. {

13.     public:

14.         int key;

15.         int value;

16.         HashEntry(int key, int value)

17.         {

18.             this->key = key;

19.             this->value = value;

20.         }

21. };

23. /*

24.  * HashMap Class Declaration

25.  */

26. class HashMap

27. {

28.     private:

29.         HashEntry **table;

30.     public:   

31.         HashMap()

32.         {

33.             table = new HashEntry * [TABLE_SIZE];

34.             for (int i = 0; i< TABLE_SIZE; i++)

35.             {

36.                 table[i] = NULL;

37.             }

38.         }

39.         /*

40.          * Hash Function

41.          */

42.         int HashFunc(int key)

43.         {

44.             return key % TABLE_SIZE;

45.         }

46.         /*

47.          * Insert Element at a key

48.          */

49.         void Insert(int key, int value)

50.         {

51.             int hash = HashFunc(key);

52.             while (table[hash] != NULL && table[hash]->key != key)

53.             {

54.                 hash = HashFunc(hash + 1);

55.             }

56.             if (table[hash] != NULL)

57.                 delete table[hash];

58.             table[hash] = new HashEntry(key, value);

59.         }

60.         /*

61.          * Search Element at a key

62.          */

63.         int Search(int key)

64.         {

65.             int  hash = HashFunc(key);

66.             while (table[hash] != NULL && table[hash]->key != key)

67.             {

68.                 hash = HashFunc(hash + 1);

69.             }

70.             if (table[hash] == NULL)

71.                 return -1;

72.             else

73.                 return table[hash]->value;

74.         }

76.         /*

77.          * Remove Element at a key

78.          */

79.         void Remove(int key)

80.         {

81.             int hash = HashFunc(key);

82.             while (table[hash] != NULL)

83.             {

84.                 if (table[hash]->key == key)

85.                     break;

86.                 hash = HashFunc(hash + 1);

87.             }

88.             if (table[hash] == NULL)

89.             {

90.                 cout<<"No Element found at key "<<key<<endl;

91.                 return;

92.             }

93.             else

94.             {

95.                 delete table[hash];

96.             }

97.             cout<<"Element Deleted"<<endl;

98.         }

99.         ~HashMap()

100.         {

101.             for (int i = 0; i < TABLE_SIZE; i++)

102.             {

103.                 if (table[i] != NULL)

104.                     delete table[i];

105.                 delete[] table;

106.             }

107.         }

108. };

109. /*

110.  * Main Contains Menu

111.  */

112. int main()

113. {

114.     HashMap hash;

115.     int key, value;

116.     int choice;

117.     while (1)

118.     {

119.         cout<<"\n----------------------"<<endl;

120.         cout<<"Operations on Hash Table"<<endl;

121.         cout<<"\n----------------------"<<endl;

122.         cout<<"1.Insert element into the table"<<endl;

123.         cout<<"2.Search element from the key"<<endl;

124.         cout<<"3.Delete element at a key"<<endl;

125.         cout<<"4.Exit"<<endl;

126.         cout<<"Enter your choice: ";

127.         cin>>choice;

128.         switch(choice)

129.         {

130.         case 1:

131.             cout<<"Enter element to be inserted: ";

132.             cin>>value;

133.             cout<<"Enter key at which element to be inserted: ";

134.             cin>>key;

135.             hash.Insert(key, value);

136.             break;

137.         case 2:

138.             cout<<"Enter key of the element to be searched: ";

139.             cin>>key;

140.             if (hash.Search(key) == -1)

141.             {

142.                 cout<<"No element found at key "<<key<<endl;

143.                 continue;

144.             }

145.             else

146.             {

147.                 cout<<"Element at key "<<key<<" : ";

148.                 cout<<hash.Search(key)<<endl;

149.             }

150.             break;

151.         case 3:

152.             cout<<"Enter key of the element to be deleted: ";

153.             cin>>key;

154.             hash.Remove(key);

155.             break;

156.         case 4:

157.             exit(1);

158.         default:

159.            cout<<"\nEnter correct option\n";

160.        }

161.     }

162.     return 0;

163. }