[LC] 706. Design HashMap

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.

Example:

MyHashMap hashMap = new MyHashMap();
hashMap.put(1, 1);          
hashMap.put(2, 2);         
hashMap.get(1);            // returns 1
hashMap.get(3);            // returns -1 (not found)
hashMap.put(2, 1);          // update the existing value
hashMap.get(2);            // returns 1 
hashMap.remove(2);          // remove the mapping for 2
hashMap.get(2);            // returns -1 (not found) 

class MyHashMap {
    private int SIZE = 1000000;
    private ListNode[] nodes;

    /** Initialize your data structure here. */
    public MyHashMap() {
        nodes = new ListNode[SIZE];
    }
    
    /** value will always be non-negative. */
    public void put(int key, int value) {
        int index = getIndex(key);
        if (nodes[index] == null) {
            nodes[index] = new ListNode(-1, -1);
        }
        ListNode prev = findNext(nodes[index], key);
        if (prev.next == null) {
            prev.next = new ListNode(key, value);
        } else {
            prev.next.val = value;
        }
    }
    
    /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
    public int get(int key) {
        int index = getIndex(key);
        if (nodes[index] == null) {
            return -1;
        }
        ListNode prev = findNext(nodes[index], key);
        if (prev.next == null) {
            return -1;
        }
        return prev.next.val;
    }
    
    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
    public void remove(int key) {
        int index = getIndex(key);
        if (nodes[index] == null) {
            return;
        }
        ListNode prev = findNext(nodes[index], key);
        if (prev.next == null) {
            return;
        }
        prev.next = prev.next.next;
    }
    
    private int getIndex(int key) {
        return Integer.hashCode(key) % SIZE;
    }
    
    private ListNode findNext(ListNode cur, int key) {
        while (cur.next != null && cur.next.key != key) {
            cur = cur.next;
        }
        return cur;
    }
}

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

/**
 * Your MyHashMap object will be instantiated and called as such:
 * MyHashMap obj = new MyHashMap();
 * obj.put(key,value);
 * int param_2 = obj.get(key);
 * obj.remove(key);
 */