Lecture 7 Hashing Table I
Hash
|---Hash function: ?Division,?Multiplication
|---Collision: ?Chaining,?Open addressing(Linear,Double hasing)
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Symbol-table problem:
Table S holding n records
pointer --> key|satelite data (record)
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Hashing:
Hash function h maps keys “randomly”?into slots of table T.
Problem: Collision.
When a record to be inserted maps to an already occupied slot, a collision occurs.
Resolving collisions by chaining.
Idea: link records in same slot into list.
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Choosing a hash function:
--Should distribute keys uniformly into slot
--Regularity in key distributions should not affect uniformly.
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除法不會(huì)考慮全部的數(shù)位,如10010,如果divisor是2的話,只和最后一位有關(guān)系。
除法比乘法的計(jì)算過程多循環(huán),即除法比乘法慢。
上面更正:
A位于2的w-1次方至w次方之間。
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