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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 .
For negative integer in hash table, the position can be calculated as follow:
Given [null, 21->9->null, 14->null, null],
return [null, 9->null, null, null, null, 21->null, 14->null, null]
1 /** 2 * Definition for ListNode 3 * public class ListNode { 4 * int val; 5 * ListNode next; 6 * ListNode(int x) { 7 * val = x; 8 * next = null; 9 * } 10 * } 11 */ 12 public class Solution { 13 /** 14 * @param hashTable: A list of The first node of linked list 15 * @return: A list of The first node of linked list which have twice size 16 */ 17 public ListNode[] rehashing(ListNode[] hashTable) { 18 if (hashTable == null || hashTable.length == 0) return hashTable; 19 20 ListNode[] newHT = new ListNode[hashTable.length * 2]; 21 22 for (int i = 0; i < hashTable.length; i++) { 23 ListNode current = hashTable[i]; 24 while (current != null) { 25 ListNode next = current.next; 26 current.next = null; 27 add(newHT, current); 28 current = next; 29 } 30 } 31 return newHT; 32 } 33 34 public void add(ListNode[] hashTable, ListNode node) { 35 int index = node.val % hashTable.length; 36 if (index < 0) { 37 index = hashTable.length + index; 38 } 39 if (hashTable[index] == null) { 40 hashTable[index] = node; 41 } else { 42 ListNode current = hashTable[index]; 43 while (current.next != null) { 44 current = current.next; 45 } 46 current.next = node; 47 } 48 } 49 };
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原文地址：http://www.cnblogs.com/beiyeqingteng/p/5697757.html
