Week 10 Workshop 7 Linear Data Structures – Part 3 Application - Hashing

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Question English
Answer English

what is hashing?
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Hashing involves using an array for the efficient storage and retrieval of information

what is the idea effeicency for hashing for storage and retrival?
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O(1)

how are collisions resolved?
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Collision is resolved by finding a free location. Next location (1) is still free - use this location. Key 10 maps to position 2

what defines a " good hash function"
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A good hash function must: Quick and easy to compute Minimise collisions Achieve an even distribution of keys Aim: Efficiency O(1) for storage and retrieval of data

what is truncation?
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Ignores parts of the key and uses remaining parts as the hash value. Fast but can fail to distribute keys uniformly.

what is folding?
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Split key into several parts and then combine the parts to obtain hash value. Often gives better spread than truncation.

what is Modula Arithmetic?
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Divide key by table size - use remainder as the hash value For good spread - table size must be prime.

what is Collision Resolution with Chaining
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Uses singly linked lists to resolve the collisions.

what is Collision Resolution with Open Addressing using Linear Rehash or Linear Probing
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A linear search of the table from the hashed position is used to find an empty slot.

what is Collision Resolution with Open Addressing using Quadratic Rehash or Quadratic Probing
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The following slots are tried to find an empty slot: h + i2 (mod table size) for i = 1,2,3... ie: slots tried are: h, h+1, h+4, h+9, h+16 ...... (mod table size) Works well if the table size is prime.

what is Collision Resolution with Open Addressing using Add the hash Rehash
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The hash value is added to the hashed value repetitively to find an empty slot. ie: slots tried are: h, 2h, 3h, 4h, ... (mod table size) Works well if the table size is prime.

what is Collision Resolution with Open Addressing using random Rehash
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a pseudo‑random number generator is used to obtain the increments Uses a seed to initiate the sequence of random numbers. Excellent in avoiding collisions but slower


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