Leetcode 705.设计哈希集合

原题链接：Leetcode 705. Design HashSet

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

Implement MyHashSet class:

• void add(key) Inserts the value key into the HashSet.
• bool contains(key) Returns whether the value key exists in the HashSet or not.
• void remove(key) Removes the value key in the HashSet. If key does not exist in the HashSet, do nothing.

Example 1:

Input
["MyHashSet", "add", "add", "contains", "contains", "add", "contains", "remove", "contains"]
[[], [1], [2], [1], [3], [2], [2], [2], [2]]
Output
[null, null, null, true, false, null, true, null, false]

Explanation
MyHashSet myHashSet = new MyHashSet();
myHashSet.add(1);      // set = [1]
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(1); // return True
myHashSet.contains(3); // return False, (not found)
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(2); // return True
myHashSet.remove(2);   // set = [1]
myHashSet.contains(2); // return False, (already removed)

Constraints:

• 0 <= key <= 10⁶
• At most 10⁴ calls will be made to add, remove, and contains.

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方法一：链地址法

思路：

用链地址法来解决冲突

C++代码：

class MyHashSet {
    
private:
    // 用链地址法 同义词在一个链表上
    vector<list<int>> hash_table;

    // 设置一个质数m
    static const int m = 11;

    // 哈希函数
    static int hash(int key) {
    
        return key % m;
    }

public:
    MyHashSet(): hash_table(m) {
    }
    
    // 插入
    void add(int key) {
    
        int h = hash(key);

        // 遍历 如果没有就插入
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
    
            if ((*it) == key) {
    
                return;
            }
        }
        hash_table[h].push_back(key);
    }
    
    // 删除
    void remove(int key) {
    
        int h = hash(key);
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
    
            if ((*it) == key) {
    
                hash_table[h].erase(it);
                return;
            }
        }
    }
    
    // 是否存在
    bool contains(int key) {
    
        int h = hash(key);
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
    
            if ((*it) == key) {
    
                return true;
            }
        }
        return false;
    }
};


/** * Your MyHashSet object will be instantiated and called as such: * MyHashSet* obj = new MyHashSet(); * obj->add(key); * obj->remove(key); * bool param_3 = obj->contains(key); */