如何优雅地利用C++编程从1乘到20?
来自:知乎,作者:小白白
链接:https://www.zhihu.com/question/365763395/answer/971009059
知乎的一个问题:
答主:小白白。
数学家版本:
(简单利索,深藏功与名)
#include <iostream>#include <cmath>int main(){
std::cout << std::tgamma(20 + 1) << std::endl;
}
语言学家版本:
(语言学家,你懂得,恨不得把所有语法特性都派上用场)
#include <iostream>#include <utility>template<std::size_t...I> constexpr auto foo(std::index_sequence<I...>) { return ((I+1) * ...); }
int main(){
std::cout << foo(std::make_index_sequence<20>()) << std::endl;
}
历史学家版本:
(void main() 有没有嗅到浓厚的历史气息?)
#include <stdio.h>void main(void){
inti;
long longj;
for(i = 1, j = 1;i <= 20; j *= i++);
printf("%lld", j);
}
敏捷开发上线1.0版本:
(可以说是非常敏捷了)
#include <stdio.h>int main(){
//printf("%d", 1*2*3*4*5*6*7*8*9*10); printf("%lld", (long long)1*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*20);
}
面向对象专家版本:
(好家伙,一个简单的问题,愣是祭出了接口、继承、虚函数、虚继承、智能指针等一大堆东西出来,这很面向对象)
#include <iostream>#include <string>#include <memory>struct IBaseInterface { virtual ~IBaseInterface() = 0;
};
inline IBaseInterface::~IBaseInterface() = default;
struct IDataProvider : virtual publicIBaseInterface {
virtual int first() = 0;
virtual int last() = 0;
virtual int next(int v) = 0;
};
struct ICalculator : virtual publicIBaseInterface {
virtual long long calc(IDataProvider *) = 0;
};
struct IPrinter : virtual publicIBaseInterface {
virtual void print(const std::string &) = 0;
};
struct ISerializer : virtual publicIBaseInterface {
virtual std::string serialize(long long value) = 0;
};
struct IRunnable : virtual publicIBaseInterface {
virtual void run() = 0;
};
class Foo : virtual publicIRunnable {
std::shared_ptr
:
Foo(std::shared_ptr<IDataProvider> dp, std::shared_ptr<ICalculator> c, std::shared_ptr<ISerializer> s, std::shared_ptr<IPrinter> p) : m_dp(std::move(dp)), m_c(std::move(c)), m_s(std::move(s)),m_p(std::move(p)) {}
void run() override { returnm_p->print(m_s->serialize(m_c->calc(m_dp.get()))); }
};
class DefaultSerializer : virtual publicISerializer {
public:
std::string serialize(long long value) override { return std::to_string(value); }
};
class StreamPrinter : virtual publicIPrinter {
std::ostream &m_os;
public:
explicit StreamPrinter (std::ostream &os) : m_os(os){}
void print(const std::string &s) override { m_os << s << std::endl; }
};
class MultiplyAccumulateCalculator : virtual publicICalculator {
public:
long long calc(IDataProvider *dp) override{
inti = dp->first();
long longj = i;
doj *= (i = dp->next(i));
while(i != dp->last());
returnj;
}
};
int main(){
struct MyDataProvider : virtual publicIDataProvider {
int first() override { return 1; }
int last() override { return 20; }
int next(int v) override { return v+1; }
};
Foo foo(std::make_shared<MyDataProvider>(), std::make_shared<MultiplyAccumulateCalculator>(), std::make_shared<DefaultSerializer>(), std::make_shared<StreamPrinter>(std::cout));
foo.run();
}
提前优化的并行版本:
(一看就是精通底层技术的大佬,把CPU拿捏得死死的)
#include <iostream>#include <xmmintrin.h>double foo(int x){
__m128 a = {1.0f, 2.0f, 3.0f, 4.0f};
__m128 b = {4.0f, 4.0f, 4.0f, 4.0f};
__m128 c = {1.0f, 1.0f, 1.0f, 1.0f};
for(int i = 0; i < x / 4; ++i, a = _mm_add_ps(a, b))
c = _mm_mul_ps(c, a);
for(int i = x % 4; i < 4; ++i)
a[i] = 1.0f;
c = _mm_mul_ps(c, a);
return (double)c[0] * (double)c[1] * (double)c[2] * (double)c[3];
}
int main(){
std::cout << foo(20) << std::endl;
}
黑魔法版本:
(能看懂这段代码的,都不是普通人!)
#include <iostream>#include <numeric>#include <vector>#include <functional>int main(){
std::vector<int> v(std::atoi(std::end(__DATE__) - (__LINE__) / 2) - 1); // 2021年,第六行 std::iota(v.begin(), v.end(), 1);
std::cout << std::accumulate(v.begin(), v.end(), 1ull, std::multiplies<>()) << std::endl;
}
“宏孩儿”元编程版:
(当年看各种C++框架中,排山倒海一样的宏定义,简直令人发指)
#include <boost/preprocessor.hpp>// 由于boost.preprocessor仅提供255以下的整数运算// 所以使用sequence来 (十位个位)(千位百位)(十万位万位) 的方式来表示大整数。// 不进位加法:(77)(66)(55) + (44)(33)(22) = (121)(99)(77)#define PP_ADD_N_N_CARRY_OP(R, DATA, I, ELEM) (BOOST_PP_ADD(BOOST_PP_SEQ_ELEM(I, DATA), ELEM))#define PP_ADD_N_N_CARRY(SEQ_A, SEQ_B) BOOST_PP_SEQ_FOR_EACH_I(PP_ADD_N_N_CARRY_OP, SEQ_A, SEQ_B)// 进位加法:(121)(99)(77) = (21)(0)(78)// 注意SEQ_A的长度要比SEQ_B长#definePP_ADD_N_N_OP(S, STATE, ELEM_CARRY) \
BOOST_PP_SEQ_PUSH_FRONT( \
BOOST_PP_SEQ_REPLACE(STATE, 0, BOOST_PP_MOD(BOOST_PP_ADD(BOOST_PP_SEQ_HEAD(STATE), ELEM_CARRY), 100)), \
BOOST_PP_DIV(BOOST_PP_ADD(BOOST_PP_SEQ_HEAD(STATE), ELEM_CARRY), 100) \
) #define PP_ADD_N_N(SEQ_A, SEQ_B) BOOST_PP_SEQ_REVERSE(BOOST_PP_SEQ_FOLD_LEFT(PP_ADD_N_N_OP, BOOST_PP_SEQ_NIL(0), PP_ADD_N_N_CARRY(SEQ_A, SEQ_B)))// 没什么好说的,X*N = X+X+X+X+X+...+X#define PP_MUL_N_1_EXP_OP(Z, I, DATA) (DATA)#define PP_MUL_N_1_EXP(SEQ_N, N) BOOST_PP_REPEAT(N, PP_MUL_N_1_EXP_OP, SEQ_N)#define PP_MUL_N_1_MYOP(S, STATE, ITEM) PP_ADD_N_N(STATE, ITEM)#define PP_MUL_N_1_FWD(EXP) BOOST_PP_SEQ_FOLD_LEFT(PP_MUL_N_1_MYOP, BOOST_PP_SEQ_HEAD(EXP), BOOST_PP_SEQ_TAIL(EXP))#define PP_MUL_N_1(SEQ_N, N) PP_MUL_N_1_FWD(PP_MUL_N_1_EXP(SEQ_N, N))#define FACT5 PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1((1), 2), 3), 4), 5)#define FACT10 PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(FACT5, 6), 7), 8), 9), 10)#define FACT15 PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(FACT10, 11), 12), 13), 14), 15)#define FACT20 PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(FACT15, 16), 17), 18), 19), 20)#define FACT25 PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(PP_MUL_N_1(FACT20, 21), 22), 23), 24), 25)static_assert(false, BOOST_PP_STRINGIZE(FACT10));
真·模板元编程版本
(泛型编程,码不惊人死不休)
#include <iostream>#include <iomanip>#include <type_traits>using BaseType_t = long long;
constexpr BaseType_t lgBase = 9; // 注意10000*10000刚刚好小于int的取值范围constexpr BaseType_t Base = 1000000000; // 注意10000*10000刚刚好小于int的取值范围// 大整数的表示template<BaseType_t...I> struct BigInteger { usingtype = BigInteger;
};
// 连接template<class T1, class T2> struct BI_Cat;template<BaseType_t...I1, BaseType_t...I2> struct BI_Cat <BigInteger<I1...>, BigInteger<I2...>> : BigInteger
> {};
// 去除开头的0template<class T> struct BI_Remove_Zeros :T {};
template<BaseType_t...I> struct BI_Remove_Zeros<BigInteger<0, I...>> : BI_Remove_Zeros
BigInteger<(I, X)...> {};
template<int Size> struct BI_Fill_Zeros : BI_Fill_Impl<0, std::make_index_sequence
...(I)>::type, BigInteger
, (A {};
// 非进位加法:先把两个数的位数改成一样的然后依次相加template<class A, class B, class ShouldResize> struct BI_AddNotCarry_Impl;template<BaseType_t...I1, BaseType_t...I2> struct BI_AddNotCarry_Impl <BigInteger<I1...>, BigInteger<I2...>, std::true_type> :BigInteger<(I1 + I2)...> {};
template<BaseType_t...I1, BaseType_t...I2> struct BI_AddNotCarry_Impl
BI_AddNotCarry_Impl<
typename BI_Resize<BigInteger<I1...>, int_min<sizeof...(I1), sizeof...(I2)>::value>::type,
typename BI_Resize<BigInteger<I2...>, int_min<sizeof...(I1), sizeof...(I2)>::value>::type,
std::true_type
>{};
template<class A, class B> struct BI_AddNotCarry;template<BaseType_t...I1, BaseType_t...I2> struct BI_AddNotCarry
...(I2)>> {};
// 判断是否为0template<class Y> struct BI_IsZero;template<BaseType_t...I> struct BI_IsZero<BigInteger<I...>> : std::bool_constant<((I == 0) && ...)> {};
// 自动进位template<class A> struct BI_Carry;template<class A, class B> struct BI_Add : BI_Carry<typenameBI_AddNotCarry::type> {};
template<class Mod, class Div, class ShouldCalc = typename BI_IsZero<Div>::type> struct BI_Carry_Impl;template<class Mod, class Div> struct BI_Carry_Impl<Mod, Div, std::true_type> :Mod {};
template<class Mod, class Div> struct BI_Carry_Impl : BI_Add<Mod, typenameBI_SHL
BI_Carry_Impl
BI_Carry
>::type, X> {};
template<> struct BI_Fact<0> : BigInteger<1> {};
templatestd::ostream &operator<<(std::ostream &out, BigInteger
::setw(lgBase)), ...);
}
int main(){
std::cout << typename BI_Fact<20>::type() << std::endl;
}--- EOF ---推荐↓↓↓相关文章
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