nPr 排列法

這方法會比旋轉要來得快

#include <functional>   // std::function
#include <memory>       // std::shared_ptr
#include <vector>
#include <iostream>

using namespace std;

// n 取 r 做排列
// 採用逆時旋轉排列法
// 必須 n >= r
class Permutation_nPr
{
  // 回報結果
  function<void(const shared_ptr<vector<unsigned char> > &, size_t)> 
    m_Report;
  // 放置要排列的數字
  shared_ptr <vector<unsigned char> > m_Digital_Array;
  // 要做排列的數目值
  size_t m_r;

  void v(size_t n, size_t r)
  {
    if (r == 0)
      m_Report(m_Digital_Array, m_r);
    else
      v(n - 1, r - 1);

    for (size_t j = n; j > 0; --j)
    {
      {
        unsigned char tmp = m_Digital_Array->at(n);
        m_Digital_Array->at(n) = m_Digital_Array->at(j-1);
        m_Digital_Array->at(j - 1) = tmp;
      }

      if (r == 0)
        m_Report(m_Digital_Array, m_r);
      else
        v(n - 1, r - 1);

      {
        unsigned char tmp = m_Digital_Array->at(n);
        m_Digital_Array->at(n) = m_Digital_Array->at(j-1);
        m_Digital_Array->at(j - 1) = tmp;
      }
    }
  }

public:
  Permutation_nPr(
   const function<void(const shared_ptr<vector<unsigned char> > &, size_t)>
      &Receive
  ):m_Report(Receive)
  {}

  void nPr(size_t n, size_t r)
  {
    m_r = r;
    m_Digital_Array =
       shared_ptr<vector<unsigned char> >(new vector<unsigned char>(n));
    size_t i = n;
    while (i--)
    {
      m_Digital_Array->at(i) = i;
    }
    v(n - 1, r - 1);
  }
};



class MsgShow
{
  int N{1};
public:
  void ResetN(){N = 1;}
  void operator()(
    const shared_ptr<vector<unsigned char> > &Digital_Array, size_t r)
  {
    cout << N << ":\t";
    for (size_t i = Digital_Array->size() - 1; r > 0; --i, --r)
      cout << (int)Digital_Array->at(i) << ' ';
    cout << endl;
    ++N;
  }
};

int main()
{
  MsgShow Report;
  Permutation_nPr P(Report);

  cout << '\n' << "4P3 排列：" << endl;
  Report.ResetN();
  P.nPr(4,3);

  return 0;
}

執行結果：

4P3 排列：
1:      3 2 1
2:      3 2 0
3:      3 1 2
4:      3 1 0
5:      3 0 1
6:      3 0 2
7:      2 3 1
8:      2 3 0
9:      2 1 3
10:     2 1 0
11:     2 0 1
12:     2 0 3
13:     1 2 3
14:     1 2 0
15:     1 3 2
16:     1 3 0
17:     1 0 3
18:     1 0 2
19:     0 2 1
20:     0 2 3
21:     0 1 2
22:     0 1 3
23:     0 3 1
24:     0 3 2

Process returned 0 (0x0)   execution time : 0.059 s
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