706. Design HashMap #

Problem #

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.

Problem Summary #

Design a hash map without using any built-in hash table libraries. Specifically, your design should include the following functions:

• put(key, value): Insert a (key, value) pair into the hash map. If the value corresponding to the key already exists, update this value.
• get(key): Return the value corresponding to the given key; if the map does not contain this key, return -1.
• remove(key): If this key exists in the map, delete this key-value pair.

Note:

• All values are in the range [1, 1000000].
• The total number of operations is in the range [1, 10000].
• Do not use the built-in hash library.

Solution Approach #

• Simple problem. Design a hashmap data structure that requires the 3 methods put(key, value), get(key), and remove(key). Designing a map mainly requires handling hash collisions, which are generally resolved using the chaining method.

Code #

package leetcode

const Len int = 100000

type MyHashMap struct {
	content [Len]*HashNode
}

type HashNode struct {
	key  int
	val  int
	next *HashNode
}

func (N *HashNode) Put(key int, value int) {
	if N.key == key {
		N.val = value
		return
	}
	if N.next == nil {
		N.next = &HashNode{key, value, nil}
		return
	}
	N.next.Put(key, value)
}

func (N *HashNode) Get(key int) int {
	if N.key == key {
		return N.val
	}
	if N.next == nil {
		return -1
	}
	return N.next.Get(key)
}

func (N *HashNode) Remove(key int) *HashNode {
	if N.key == key {
		p := N.next
		N.next = nil
		return p
	}
	if N.next != nil {
		N.next = N.next.Remove(key)
	}
	return N
}

/** Initialize your data structure here. */
func Constructor706() MyHashMap {
	return MyHashMap{}
}

/** value will always be non-negative. */
func (this *MyHashMap) Put(key int, value int) {
	node := this.content[this.Hash(key)]
	if node == nil {
		this.content[this.Hash(key)] = &HashNode{key: key, val: value, next: nil}
		return
	}
	node.Put(key, value)
}

/** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
func (this *MyHashMap) Get(key int) int {
	HashNode := this.content[this.Hash(key)]
	if HashNode == nil {
		return -1
	}
	return HashNode.Get(key)
}

/** Removes the mapping of the specified value key if this map contains a mapping for the key */
func (this *MyHashMap) Remove(key int) {
	HashNode := this.content[this.Hash(key)]
	if HashNode == nil {
		return
	}
	this.content[this.Hash(key)] = HashNode.Remove(key)
}

func (this *MyHashMap) Hash(value int) int {
	return value % Len
}

/**
 * Your MyHashMap object will be instantiated and called as such:
 * obj := Constructor();
 * obj.Put(key,value);
 * param_2 := obj.Get(key);
 * obj.Remove(key);
 */