leetcode-706-Design-HashMap

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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:

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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.

分析

见上一题

解决方案1(Java)

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class MyHashMap {
    final Bucket[] buckets = new Bucket[10000];
    
    int index(int key) {
        return Integer.hashCode(key) % buckets.length;
    }
    
    ListNode find(Bucket bucket, int key) {
        ListNode node = bucket.head, prev = null;
        while (node != null && node.key != key) {
            prev = node;
            node = node.next;
        }
        return prev;
    }

    /** Initialize your data structure here. */
    public MyHashMap() {
        
    }
    
    /** value will always be non-negative. */
    public void put(int key, int value) {
        int i = index(key);
        if (buckets[i] == null) {
            buckets[i] = new Bucket();
        }
        ListNode node = find(buckets[i], key);
        if (node.next == null) {
            node.next = new ListNode(key, value);
        } else {
            node.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 i = index(key);
        if (buckets[i] == null) {
            return -1;
        }
        ListNode node = find(buckets[i], key);
        return node.next == null ? -1 : node.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 i = index(key);
        if (buckets[i] == null) {
            return;
        }
        ListNode node = find(buckets[i], key);
        if (node.next == null) {
            return;
        }
        node.next = node.next.next;
    }
}

class Bucket {
        final ListNode head = new ListNode(-1, -1);
    }

class ListNode {
    int key, val;
    ListNode next;

    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);
 */

解决方案2（Golang）

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const base = 769

type entry struct {
    key, value int
}

type MyHashMap struct {
    data []list.List
}


func Constructor() MyHashMap {
    return MyHashMap{make([]list.List, base)}
}

func (this *MyHashMap) hash(key int) int {
    return key % base
}

func (this *MyHashMap) Put(key int, value int)  {
    hash := this.hash(key)
    for e := this.data[hash].Front(); e != nil ; e = e.Next() {
        if now := e.Value.(entry); now.key == key {
            e.Value = entry{key, value}
            return
        }
    }
    this.data[hash].PushBack(entry{key, value})
}


func (this *MyHashMap) Get(key int) int {
    hash := this.hash(key)
    for e := this.data[hash].Front(); e != nil ; e = e.Next() {
        if now := e.Value.(entry); now.key == key {
            return now.value
        }
    }
    return -1
}


func (this *MyHashMap) Remove(key int)  {
    hash := this.hash(key)
    for e := this.data[hash].Front(); e != nil ; e = e.Next() {
        if now := e.Value.(entry); now.key == key {
            this.data[hash].Remove(e)
        }
    }
}


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

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