std::greater by key (tools/greater_by.hpp)

• View this file on GitHub
• View document part on GitHub
• Last update: 2021-03-29 00:30:01+09:00
• Include: #include "tools/greater_by.hpp"

It compares two values by a given key selector.

Usage

std::sort(a.begin(), a.end(), tools::greater_by([](int a_i) { return std::abs(x); }));

License

• CC0

Author

• anqooqie

Constructor

tools::greater_by<F> comp(F f);

It creates a comparator.

Constraints

• None

Time Complexity

• $O(1)$

operator()

template <typename T>
bool comp(T x, T y);

It returns true if f(x) > f(y). Otherwise, it returns false.

Constraints

• f has operator()(T x)
• f(x) is comparable

Time Complexity

• $O(1)$ if f(x) takes constant time

Required by

• Product of polynomials (tools/polynomial_product.hpp)
• Prim's algorithm (tools/prim.hpp)

Verified with

• tests/polynomial_product.test.cpp
• tests/prim/basic.test.cpp
• tests/prim/unconnected.test.cpp

Code

#ifndef TOOLS_GREATER_BY_HPP
#define TOOLS_GREATER_BY_HPP

namespace tools {

  template <class F>
  class greater_by {
  private:
    F selector;

  public:
    greater_by(const F& selector) : selector(selector) {
    }

    template <class T>
    bool operator()(const T& x, const T& y) const {
      return selector(x) > selector(y);
    }
  };
}

#endif

#line 1 "tools/greater_by.hpp"



namespace tools {

  template <class F>
  class greater_by {
  private:
    F selector;

  public:
    greater_by(const F& selector) : selector(selector) {
    }

    template <class T>
    bool operator()(const T& x, const T& y) const {
      return selector(x) > selector(y);
    }
  };
}

Back to top page