search/algos.hpp


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#pragma once
#include "base/base.hpp"

#include "std/algorithm.hpp"
#include "std/vector.hpp"


namespace search
{

namespace impl
{
  struct LS
  {
    size_t prevDecreasePos, decreaseValue;
    size_t prevIncreasePos, increaseValue;

    LS(size_t i)
    {
      prevDecreasePos = i;
      decreaseValue = 1;
      prevIncreasePos = i;
      increaseValue = 1;
    }
  };
}

template <class T, class OutIterT, class CompT>
void LongestSubsequence(vector<T> const & in, OutIterT out, CompT cmp)
{
  if (in.empty())
    return;

  vector<impl::LS> v;
  v.reserve(in.size());
  for (size_t i = 0; i < in.size(); ++i)
    v.push_back(impl::LS(i));

  size_t res = 1;
  size_t pos = 0;
  for (size_t i = 0; i < v.size(); ++i)
  {
    for (size_t j = i+1; j < v.size(); ++j)
    {
      if (cmp.Less(in[i], in[j]) && v[i].increaseValue + 1 >= v[j].increaseValue)
      {
        v[j].increaseValue = v[i].increaseValue + 1;
        v[j].prevIncreasePos = i;
      }

      if (cmp.Greater(in[i], in[j]) && v[i].decreaseValue + 1 >= v[j].decreaseValue)
      {
        v[j].decreaseValue = v[i].decreaseValue + 1;
        v[j].prevDecreasePos = i;
      }

      size_t const m = max(v[j].increaseValue, v[j].decreaseValue);
      if (m > res)
      {
        res = m;
        pos = j;
      }
    }
  }

  bool increasing = true;
  if (v[pos].increaseValue < v[pos].decreaseValue)
    increasing = false;

  while (res-- > 0)
  {
    *out++ = in[pos];

    if (increasing)
      pos = v[pos].prevIncreasePos;
    else
      pos = v[pos].prevDecreasePos;
  }
}

}