Description:
Design 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.
Solution:
思路和hashmap实现思路一样，事实上，hashset底层就是基于hashmap的。
class MyHashSet {
ListNode[] nodes = new ListNode[1000001];
private class ListNode{
int val;
ListNode next;
ListNode(int val) {
this.val = val;
}
}
private int getIndex(int val){
return Integer.hashCode(val) % 1000000;
}
//return the node before val, or return the final node
private ListNode getElem(int val){
int index = getIndex(val);
//if null, then create the root(but not use it)
if(nodes[index] == null){
nodes[index] = new ListNode(-1);
return nodes[index];
}
ListNode previous = nodes[index];
while(previous.next != null && previous.next.val != val){
previous = previous.next;
}
return previous;
}
/** Initialize your data structure here. */
public MyHashSet() {
}
public void add(int key) {
ListNode pre = getElem(getIndex(key));
if(pre.next == null) {
pre.next = new ListNode(key);
} else {
pre.next.val = key;
}
}
public void remove(int key) {
ListNode pre = getElem(getIndex(key));
if(pre.next == null) {
} else {
pre.next = pre.next.next;
}
}
/** Returns true if this set contains the specified element */
public boolean contains(int key) {
ListNode pre = getElem(getIndex(key));
if(pre.next == null) {
return false;
} else {
return true;
}
}
}
/**
* Your MyHashSet object will be instantiated and called as such:
* MyHashSet obj = new MyHashSet();
* obj.add(key);
* obj.remove(key);
* boolean param_3 = obj.contains(key);
*/