leetcode-705-Design-HashSet

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描述

Design a HashSet without using any built-in hash table libraries.

To be specific, your design should include these functions:

  • add(value): Insert a value into the HashSet.
  • contains(value) : Return whether the value exists in the HashSet or not.
  • remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.

Example:

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MyHashSet hashSet = new MyHashSet();
hashSet.add(1);         
hashSet.add(2);         
hashSet.contains(1);    // returns true
hashSet.contains(3);    // returns false (not found)
hashSet.add(2);          
hashSet.contains(2);    // returns true
hashSet.remove(2);          
hashSet.contains(2);    // returns false (already removed)

Note:

  • All 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 HashSet library.

分析

题目要求自己实现一个 HashSet，不能使用内置的库。key 的范围在 [0, 1000000]，可以用数组来当做哈希表，解决哈希冲突可以使用链地址法和开放寻址法，这里我们使用链表来实现链地址法。

下一题 706. Design HashMap 简直和这道题一模一样，只不过下一题是实现 HashMap，就两行代码的差别。

解决方案1(Java)

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class MyHashSet {
    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 MyHashSet() {
        
    }
    
    public void add(int key) {
        int i = index(key);
        if (buckets[i] == null) {
            buckets[i] = new Bucket();
        }
        ListNode prev = find(buckets[i], key);
        if (prev.next == null) {
            prev.next = new ListNode(key, 1);
        } else {
            prev.next.val = 1;
        }
    }
    
    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;
    }
    
    /** Returns true if this set contains the specified element */
    public boolean contains(int key) {
        int i = index(key);
        if (buckets[i] == null) {
            return false;
        }
        ListNode node = find(buckets[i], key);
        if (node.next == null) {
            return false;
        }
        return true;
    }
}

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 MyHashSet object will be instantiated and called as such:
 * MyHashSet obj = new MyHashSet();
 * obj.add(key);
 * obj.remove(key);
 * boolean param_3 = obj.contains(key);
 */

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