> For the complete documentation index, see [llms.txt](https://wentao-shao.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://wentao-shao.gitbook.io/leetcode/data-structure/706.design-hashmap.md).

# 706.Design-HashMap

## 706. Design HashMap

## 题目地址

<https://leetcode.com/problems/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.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.
```

## 代码

Approach 1: Modulo + Array

```java
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() {
    this.bucket = new LinkedList<Pair<Integer, Integer>>();
  }

  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) {
      this.bucket.add(new Pair<Integer, Integer>(key, value));
    }
  }

  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++) {
      this.hash_table.add(new Bucket());
    }
  }

  /** 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);
 */
```


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