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) 

Note:

• All keys and 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 HashMap library.

My answer:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94

class MyHashMap { // array + chaining, I missed case: existing key is updated // use array, and each element is a list, containing nodes, each of node has key and value associated class Node { public int key; public int value; Node (int key, int value) { this.key = key; this.value = value; } } class ListNode { public List<Node> nodes; public ListNode () { nodes = new ArrayList<Node>(); } } private ListNode[] elements; /** Initialize your data structure here. */ public MyHashMap() { elements = new ListNode[10000]; } private int getIndex(int key) { return key % elements.length; } /** value will always be non-negative. */ public void put(int key, int value) { int index = getIndex(key); ListNode nodeList = elements[index]; if (nodeList == null) { nodeList = new ListNode(); } boolean existed = false; for (Node node : nodeList.nodes) { if (node.key == key) { node.value = value; existed = true; } } if (!existed) { nodeList.nodes.add(new Node(key, value)); } elements[index] = nodeList; } /** 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); ListNode nodeList = elements[index]; if (nodeList == null) { return -1; } for (Node node : nodeList.nodes) { if (node.key == key) { return node.value; } } return -1; } /** 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); ListNode nodeList = elements[index]; if (nodeList == null || nodeList.nodes.isEmpty()) { return; } int nodeIndex = -1; for (int i = 0; i < nodeList.nodes.size(); i ++) { if (nodeList.nodes.get(i).key == key) { nodeIndex = i; break; } } if (nodeIndex != -1) { nodeList.nodes.remove(nodeIndex); } } } /** * 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); */