DesignHashMap.java

Design a HashMap without using any built-in hash table libraries.

To be specific, your design should include these functions:

put(key, value) : Insert a (key, value) pair into the HashMap. If the value already
exists in the HashMap, update the value.

get(key): Returns the value to which the specified key is mapped, or -1 if this map contains 
no mapping for the key.

remove(key) : Remove the mapping for the value key if this map contains the mapping for the key.

//Intution use linked list to handle collisions, 
//need hashcode to return same value for EQUAL OBJECTS 

class MyHashMap {
 final ListNode[] nodes = new ListNode[10000];

        public void put(int key, int value) {
            int i = idx(key);
            if (nodes[i] == null)
                nodes[i] = new ListNode(-1, -1);
            ListNode prev = find(nodes[i], key);
            if (prev.next == null)
                prev.next = new ListNode(key, value);
            else prev.next.val = value;
        }

        public int get(int key) {
            int i = idx(key);
            if (nodes[i] == null)
                return -1;
            ListNode node = find(nodes[i], key);
            return node.next == null ? -1 : node.next.val;
        }

        public void remove(int key) {
            int i = idx(key);
            if (nodes[i] == null) return;
            ListNode prev = find(nodes[i], key);
            if (prev.next == null) return;
            prev.next = prev.next.next;
        }

        int idx(int key) { return Integer.hashCode(key) % nodes.length;}

        ListNode find(ListNode bucket, int key) {
            ListNode node = bucket, prev = null;
            while (node != null && node.key != key) {
                prev = node;
                node = node.next;
            }
            return prev;
        }

        class ListNode {
            int key, val;
            ListNode next;

            ListNode(int key, int val) {
                this.key = key;
                this.val = val;
            }
        }
}