C++STL哈希，Python哈希，Java哈希

哈希表 - 用法

我提供了在 Java，C++ 和 Python 中使用哈希集的示例。 如果你不熟悉哈希集的用法，那么通过这一示例将会很有帮助。

//C++
#include <iostream>
#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;
    }
}

//java
// "static void main" must be defined in a public class.
public class Main {
    public static void main(String[] args) {
        // 1. initialize the hash set
        Set<Integer> hashSet = new HashSet<>();     
        // 2. add a new key
        hashSet.add(3);
        hashSet.add(2);
        hashSet.add(1);
        // 3. remove the key
        hashSet.remove(2);        
        // 4. check if the key is in the hash set
        if (!hashSet.contains(2)) {
            System.out.println("Key 2 is not in the hash set.");
        }
        // 5. get the size of the hash set
        System.out.println("The size of has set is: " + hashSet.size());     
        // 6. iterate the hash set
        for (Integer i : hashSet) {
            System.out.print(i + " ");
        }
        System.out.println("are in the hash set.");
        // 7. clear the hash set
        hashSet.clear();
        // 8. check if the hash set is empty
        if (hashSet.isEmpty()) {
            System.out.println("hash set is empty now!");
        }
    }
}

#python
# 1. initialize the hash set
hashset = set() 
# 2. add a new key
hashset.add(3)
hashset.add(2)
hashset.add(1)
# 3. remove a key
hashset.remove(2)
# 4. check if the key is in the hash set
if (2 not in hashset):
    print("Key 2 is not in the hash set.")
# 5. get the size of the hash set
print("Size of hashset is:", len(hashset)) 
# 6. iterate the hash set
for x in hashset:
    print(x, end=" ")
print("are in the hash set.")
# 7. clear the hash set
hashset.clear()                         
print("Size of hashset:", len(hashset))