【数据结构基础

原题链接：Leetcode 706. Design HashMap

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

Implement the MyHashMap class:

MyHashMap() initializes the object with an empty map.

• void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key - already exists in the map, update the corresponding value.
• int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
• void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.

Example 1:

Input
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]

Explanation
MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1);    // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3);    // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2);    // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2);    // return -1 (i.e., not found), The map is now [[1,1]]

Constraints:

• 0 <= key, value <= 10⁶
• At most 10⁴ calls will be made to put, get, and remove.

链地址法解决冲突

class MyHashMap {
private:
    // 链地址法
    vector>> hash_table;

    // m为设置的质数
    static const int m = 11;

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

public:
    MyHashMap(): hash_table(m) {}
    
    // 插入键值对
    void put(int key, int value) {
        int h = hash(key);
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
            if ((*it).first == key) {
                (*it).second = value;
                return;
            }
        }
        hash_table[h].push_back(make_pair(key, value));
    }
    
    // 返回值
    int get(int key) {
        int h = hash(key);
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
            if ((*it).first == key) {
                return (*it).second;
            }
        }
        return -1;
    }
    
    // 移除
    void remove(int key) {
        int h = hash(key);
        for (auto it = hash_table[h].begin(); it != hash_table[h].end(); it++) {
            if ((*it).first == key) {
                hash_table[h].erase(it);
                return;
            }
        }
    }
};