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# 706.Design-HashMap

## 题目描述

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.put(2, 1); // update the existing value
hashMap.get(2); // returns 1
hashMap.remove(2); // remove the mapping for 2
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.

## 代码

Approach 1: Modulo + Array
class Pair<U, V> {
public U first;
public V second;
public Pair(U first, V second) {
this.first = first;
this.second = second;
}
}
// collision handling
class Bucket {
private List<Pair<Integer, Integer>> bucket;
public Bucket() {
}
public Integer get(Integer key) {
for (Pair<Integer, Integer> pair : this.bucket) {
if (pair.first.equals(key)) {
return pair.second;
}
}
return -1;
}
public void update(Integer key, Integer value) {
boolean found = false;
for (Pair<Integer, Integer> pair : this.bucket) {
if (pair.first.equesl(key)) {
pair.second = value;
found = true;
}
}
if (!found) {
}
}
public void remove(Integer key) {
for (Pair<Integer, Integer> pair : this.bucket) {
if (pair.first.equals(key)) {
this.bucket.remove(pair);
break;
}
}
}
}
class MyHashMap {
// hash function design
private int key_space;
private List<Bucket> hash_table;
/** Initialize your data structure here. */
public MyHashMap() {
this.key_space = 2069;
this.hash_table = new ArrayList<Bucket>();
for (int i = 0; i < this.key_space; i++) {
}
}
/** value will always be non-negative. */
public void put(int key, int value) {
int hash_key = key % this.key_space;
this.hash_table.get(hash_key).update(key, 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 hash_key = key % this.key_space;
return this.hash_table.get(hash_key).get(key);
}
/** Removes the mapping of the specified value key if this map contains a mapping for the key */
public void remove(int key) {
int hash_key = key % this.hash_space;
this.hash_table.get(hash_key).remove(key);
}
}
/**
* 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);
*/