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# More on Hash Tables - PowerPoint PPT Presentation

More on Hash Tables. Andy Wang Data Structures, Algorithms, and Generic Programming. Why Hash Tables?. Arguments Linear search is simple Hash table does not save that much time Counter arguments What if the data volume is high? (internet routers)

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## More on Hash Tables

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### More on Hash Tables

Andy Wang

Data Structures, Algorithms, and Generic Programming

Why Hash Tables?
• Arguments
• Linear search is simple
• Hash table does not save that much time
• Counter arguments
• What if the data volume is high? (internet routers)
• What if the data set if large? (yellow page)
Steps to Build a Hash Table

1. Build a table to support basic operations

• Insert
• Lookup
• Remove

2. Use a hash function to determine the table entry

3. Add mechanisms to handle collisions

Hash(name)

Insert()

Icarumba!

Hash Table

Remove()

Hash Table

Lookup()

Hash Table

Hash(name)

Tricky Case…

Oops…

Hash Table

To Handle Tricky Cases

Insert(…) {

if (Lookup(…) == false) {

// insert

}

}

Remove(…) {

if (entry[hash] empty || entry[hash] != key)

// linear search for the entry

}

}

To Handle Tricky Cases

Lookup(…) {

if (entry[hash] empty || entry[hash] != key)

// linear search for the entry

}

}