Problem
esign a HashSet without using any built-in hash table libraries.
To be specific, your design should include these functions:
add(value): Insert a value into the HashSet.
contains(value) : Return whether the value exists in the HashSet or not.
remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.
Example:
MyHashSet hashSet = new MyHashSet();
hashSet.add(1);
hashSet.add(2);
hashSet.contains(1); // returns true
hashSet.contains(3); // returns false (not found)
hashSet.add(2);
hashSet.contains(2); // returns true
hashSet.remove(2);
hashSet.contains(2); // returns false (already removed)
Note:
All values will be in the range of [0, 1000000].
The number of operations will be in the range of [1, 10000].
Please do not use the built-in HashSet library.
Solution
class MyHashSet {
class Bucket {
ListNode head = new ListNode(-1);
}
class ListNode {
int key;
ListNode next;
ListNode(int key) {
this.key = key;
}
}
int size = 10000;
Bucket[] buckets = new Bucket[size];
int hash(int key) {
return key%size;
}
ListNode find(Bucket bucket, int key) {
ListNode head = bucket.head;
ListNode pre = head;
while (head != null && head.key != key) {
pre = head;
head = head.next;
}
return pre;
}
public void add(int key) {
int i = hash(key);
if (buckets[i] == null) buckets[i] = new Bucket();
ListNode pre = find(buckets[i], key);
if (pre.next == null) pre.next = new ListNode(key);
}
public void remove(int key) {
int i = hash(key);
if (buckets[i] != null) {
ListNode pre = find(buckets[i], key);
if (pre.next != null) pre.next = pre.next.next;
}
}
/** Returns true if this set contains the specified element */
public boolean contains(int key) {
int i = hash(key);
if (buckets[i] != null) {
ListNode pre = find(buckets[i], key);
return pre.next == null ? false : true;
}
return false;
}
}