Rehashing - Lintcode Java | Welkin Lan

Rehashing – Lintcode Java | Welkin Lan

Rehashing – Lintcode Java

Q:

The size of the hash table is not determinate at the very beginning. If the total size of keys is too large (e.g. size >= capacity / 10), we should double the size of the hash table and rehash every keys. Say you have a hash table looks like below:

size=3, capacity=4

[null, 21, 14, null] ↓ ↓ 9 null ↓ null

1 2 3 4 5

[null, 21, 14, null]        ↓    ↓        9   null        ↓       null

The hash function is:

int hashcode(int key, int capacity) { return key % capacity; }

1 2 3

int hashcode(int key, int capacity) {     return key % capacity; }

here we have three numbers, 9, 14 and 21, where 21 and 9 share the same position as they all have the same hashcode 1 (21 % 4 = 9 % 4 = 1). We store them in the hash table by linked list.

rehashing this hash table, double the capacity, you will get:

size=3, capacity=8

index: 0 1 2 3 4 5 6 7 hash : [null, 9, null, null, null, 21, 14, null]

1 2	index:   0    1    2    3     4    5    6   7 hash : [null, 9, null, null, null, 21, 14, null]

Given the original hash table, return the new hash table after rehashing .

Example

Given [null, 21->9->null, 14->null, null],

return [null, 9->null, null, null, null, 21->null, 14->null, null]

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