哈希表 set/map 语法

set

#include <unordered_set>                // 0. include the library

int main() {
    // 1. initialize a hash set
    unordered_set<int> hashset;   
    // 2. insert a new key
    hashset.insert(3);
    hashset.insert(2);
    hashset.insert(1);
    // 3. delete a key
    hashset.erase(2);
    // 4. check if the key is in the hash set
    if (hashset.count(2) <= 0) {
        cout << "Key 2 is not in the hash set." << endl;
    }
    // 5. get the size of the hash set
    cout << "The size of hash set is: " << hashset.size() << endl; 
    // 6. iterate the hash set
    for (auto it = hashset.begin(); it != hashset.end(); ++it) {
        cout << (*it) << " ";
    }
    cout << "are in the hash set." << endl;
    // 7. clear the hash set
    hashset.clear();
    // 8. check if the hash set is empty
    if (hashset.empty()) {
        cout << "hash set is empty now!" << endl;
    }
}

map

#include <unordered_map>                // 0. include the library

int main() {
    // 1. initialize a hash map
    unordered_map<int, int> hashmap;
    // 2. insert a new (key, value) pair
    hashmap.insert(make_pair(0, 0));
    hashmap.insert(make_pair(2, 3));
    // 3. insert a new (key, value) pair or update the value of existed key
    hashmap[1] = 1;
    hashmap[1] = 2;
    // 4. get the value of a specific key
    cout << "The value of key 1 is: " << hashmap[1] << endl;
    // 5. delete a key
    hashmap.erase(2);
    // 6. check if a key is in the hash map
    if (hashmap.count(2) <= 0) {
        cout << "Key 2 is not in the hash map." << endl;
    }
    // 7. get the size of the hash map
    cout << "the size of hash map is: " << hashmap.size() << endl; 
    // 8. iterate the hash map
    for (auto it = hashmap.begin(); it != hashmap.end(); ++it) {
        cout << "(" << it->first << "," << it->second << ") ";
    }
    cout << "are in the hash map." << endl;
    // 9. clear the hash map
    hashmap.clear();
    // 10. check if the hash map is empty
    if (hashmap.empty()) {
        cout << "hash map is empty now!" << endl;
    }
}