C++ vector

1. vector 기본 예제

#include <vector>
#include <iostream>

using namespace std;

int main() {
    vector<int> items;
    items.push_back(1);
    items.push_back(8);
    items.push_back(15);
    items.push_back(20);
    items.pop_back();
    // items.insert(시작점, 개수, 값);
    items.insert(items.end(), 2, 30);
    
    cout << "[size] : " << items.size() << endl;
    cout << "[first item] : " << items.front() << endl;
    cout << "[last item] : " << items.back() << endl;
    
    return 0;
}

2. vector 순열

#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
    vector<int> items{3, 4, 6, 8, 12};
    int len = items.size();
    
    for (int i = items.size() - 1; i >= 0; i--) {
        vector<bool> states(i, false);
        states.insert(states.begin(), len - i, true);

        do {
            cout << "[items] ";
            string value = "";
            for (int j = 0; j < states.size(); j++) {
                cout << states[j] << " ";
                
                if (states[j]) {
                    value += to_string(items[j]) + " "; 
                }
            }
            cout << ">> " << value << endl;
        }
        while (prev_permutation(states.begin(), states.end()));
    }

    return 0;
}

3. vector 개수 세기

#include <vector>
#include <iostream>
#include <set>
#include <algorithm>

using namespace std;

int main() {
    vector<int> items{3, 3, 5, 8, 5, 2, 8, 10};
    set<int> item_set(items.begin(), items.end());
    
    for (int item : item_set) {
        int item_count = count(items.begin(), items.end(), item);
        cout << item << " >> " << item_count << "\n";
    }

    return 0;
}

4. vector heap

#include<vector>
#include<iostream>
#include<algorithm>

using namespace std;

int main()
{
    int answer = 0;
    
    vector<int> items{5, 3, 8, 9, 2};
    int count = 4;

    make_heap(items.begin(), items.end());
    while (count > 0) {
        pop_heap(items.begin(), items.end());
        int max_value = items.back();
        if (max_value <= 0) break;
        
        items.pop_back();
        items.push_back(max_value - 1);
        count--;
    }

    for (int i = 0; i < items.size(); i++) {
        cout << items[i] << "\t";
    }
    cout << endl;
        
    return 0;
}