全组合 in C++

main.cpp

#include <string>
#include <vector>
#include <iostream>

using namespace std;


int combinations(int n, int k)
{
    int result = 1;
    for (int i = n - k + 1; i <= n; ++i)
    {
        result *= i;
    }
    for (int i = 2; i <= k; ++i)
    {
        result /= i;
    }
    return result;
}


vector<vector<int> > all_combination(int all, int select)
{
    if (select == 1)
    {
        vector<vector<int> > result(all);
        for (int i = 0; i < all; ++i)
        {
            result[i] = { i };
        }
        return result;
    }
    else
    {
        vector<vector<int> > result;
        result.reserve(combinations(all, select));
        for (int i = 0; i < all - select + 1; ++i)
        {
            vector<vector<int> > t = all_combination(all - i - 1, select - 1);
            for (auto it = t.begin(); it != t.end(); ++it)
            {
                vector<int> c;
                c.reserve(it->size() + 1);
                c.push_back(i);
                for (auto jt = it->begin(); jt != it->end(); ++jt)
                {
                    c.push_back(i + 1);
                }
                result.push_back(move(c));
            }
        }
        return result;
    }
}


int main()
{
    vector<vector<int> > a = all_combination(10, 3);
    for (vector<int> t : a)
    {
        for (int x : t)
            cout << x << ", ";
        cout << endl;
    }
    return 0;
}