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Rehashing.java
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106 lines (79 loc) · 3.35 KB
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/*Rehashing.java
Rehashing
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
The hash function is:
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]
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]
Note
For negative integer in hash table, the position can be calculated as follow:
•C++/Java: if you directly calculate -4 % 3 you will get -1. You can use function: a % b = (a % b + b) % b to make it is a non negative integer.
•Python: you can directly use -1 % 3, you will get 2 automatically.
Tags LintCode Copyright Hash Table
*/
/**
* Definition for ListNode
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
/**
* @param hashTable: A list of The first node of linked list
* @return: A list of The first node of linked list which have twice size
*/
public ListNode[] rehashing(ListNode[] hashTable) {
// write your code here
if (hashTable == null || hashTable.length == 0) {
return hashTable;
}
int initialSize = hashTable.length;
int size = initialSize * 2;
ListNode[] rehashed = new ListNode[size];
for (int i = 0; i < initialSize; i++) {
ListNode temp = hashTable[i];
while (temp != null) {
int newPos = (temp.val % size + size) % size;
ListNode rehash = rehashed[newPos];
if ( rehash == null) {
rehashed[newPos] = new ListNode(temp.val);
} else {
while (rehash.next != null) {
rehash = rehash.next;
}
rehash.next = new ListNode(temp.val);
}
temp = temp.next;
}
}
return rehashed;
}
}
/* Solved Wrong Case One: 93 got lost
Input
[80->null,null,null,null,null,null,null,187->null,null,49->109->null,10->50->-10->null,null,12->null,53->133->153->93->null,null,15->null,36->null,-3->null,118->null,159->139->null]
Output
[80->null,null,null,null,null,null,null,null,null,49->null,10->50->null,null,12->null,53->133->null,null,15->null,null,null,null,139->null,null,null,null,null,null,null,null,187->null,null,109->null,-10->null,null,null,153->null,null,null,36->null,-3->null,118->null,159->null]
Expected
[80->null,null,null,null,null,null,null,null,null,49->null,10->50->null,null,12->null,53->133->93->null,null,15->null,null,null,null,139->null,null,null,null,null,null,null,null,187->null,null,109->null,-10->null,null,null,153->null,null,null,36->null,-3->null,118->null,159->null]
*/