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`

<code>[null, 21, 14, null] ↓ ↓ 9 null ↓ null </code>

The hash function is:

<code>int hashcode(int key, int capacity) { return key % capacity; } </code>

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`

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

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.

Solution:

Note: For negative integer in hash table, the position can be calculated as follow:

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.

public ListNode[] rehashing(ListNode[] hashTable) { if (hashTable == null) { return null; } ListNode[] newHash = new ListNode[hashTable.length * 2]; int capacity = newHash.length; for (int i = 0; i < hashTable.length; i++) { ListNode node = hashTable[i]; while (node != null) { int index = mod(node.val, capacity); ListNode next = node.next; //need to remove the next pointer node.next = null; //if it is the first one if (newHash[index] == null) { newHash[index] = node; } else { ListNode runner = newHash[index]; while (runner.next != null) { runner = runner.next; } runner.next = node; } hashTable[i] = next; //set to its next node node = next; } } return newHash; } //For negative integer in hash table, the position can be calculated as follow: //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. public int mod(int A, int module) { return (A % module + module) % module; }