Port ruby solution to C++

Is there any way to do this in C++ especially the range section.

answer = (0..999).select { |a| a%3 ==0 || a%5==0 }
puts answer.inject { |sum, n| sum+n }

I have created my own c++ solution but using a more s开发者_JAVA百科tandard for loop and wondered if there was a cooler way to do it?

---

Template metaprogramming solution:

The following assumes the lower bound of the range is 0.

template <int N>
struct sum
{
  static const int value = sum<N-1>::value + (N % 3 == 0 || N % 5 == 0 ? N : 0);
};

template <>
struct sum<0>
{
  static const int value = 0;
};

int main(int argc, char** argv)
{
  int n = sum<999>::value;
  return 0;
}

The following will allow you to specify a range of numbers (e.g. 0-999, 20-400). I'm not a master of template metaprogramming so I couldn't think of a cleaner solution (and I did this for my own benefit and practice).

template <int N, int Upper, bool IsLast>
struct sum_range_helper
{
  static const int value = (N % 3 == 0 || N % 5 == 0 ? N : 0) + sum_range_helper<N + 1, Upper, N + 1 == Upper>::value;
};

template <int N, int Upper>
struct sum_range_helper<N, Upper, true>
{
  static const int value = (N % 3 == 0 || N % 5 == 0 ? N : 0);
};

template <int Lower, int Upper>
struct sum_range
{
  static const int value = sum_range_helper<Lower, Upper, Lower == Upper>::value;
};

int main(int argc, char** argv)
{
  int n = sum_range<0, 999>::value;
  return 0;
}

---

Untested code. Uses C++ 0x feature (lambda function and iota)

vector<int> v(1000);

//fill the vector
iota(v.begin(),v.end(),0);

v.erase(remove_if(v.begin(),v.end(),[](int a) { return !(a%3 && a%5); }),v.end());
int sum = accumulate(v.begin(),v.end(),0);

---

The equivalent C++ program would be:

#include <iostream>
using namespace std;

int main() {
  int sum = 0;
  for (int i=0; i <= 999; i++) {
    if (i%3 == 0 || i%5 == 0)
      sum += i;
  }
  cout << sum;
  return 0;
}

---

Here's a cool C version:

#include <stdio.h>

#define LAMBDA(body, ...) ({ int _(__VA_ARGS__) { return (body); }; _; })

int range(int* arr, int start, int end) {
    (*arr = start) < end && range(arr + 1, start + 1, end);
}

void select(int* arr, int count, int(*fn)(int)) {
    int i;
    for(i = 0; i < count; i++)
        if(!fn(arr[i]))
            arr[i] = 0;
}

int inject(int* arr, int count, int(*fn)(int,int)) {
    int acc = arr[0], i;
    for(i = 1; i < count; i++)
        acc = fn(acc, arr[i]);
    return acc;
}

int main()
{
    int numbers[1000];

    range(numbers, 1, 1000);
    select(numbers, 1000, LAMBDA(a % 3 == 0 || a % 5 == 0, a));
    printf("%d\n", inject(numbers, 1000, LAMBDA(a + b, a, b)));
}

http://codepad.org/eUKFAvkc