华为面试题(8分钟写出代码)

有两个数组a,b，大小都为n,数组元素的值任意，无序；

要求：通过交换a,b中的元素，使数组a元素的和与数组b元素的和之间的差最小

题目来源：http://bbs.chinaunix.net/thread-855126-1-1.html

#include
#include
#include
#include
#include

template
std::ostream& operator<<(std::ostream &ostr, std::array const &data){
	for (size_t i = 0; i != N; ++i) ostr << data[i] << " ";
	return ostr;
}

int main(){
	using type = int;
	size_t const n = 3;
	std::array a, b;
	
	std::mt19937 gen((std::random_device())());
	std::uniform_int_distribution rand(0, n*n);// 小心溢出
	
	for (size_t i = 0; i != n; ++i) {
		a[i] = rand(gen);
		b[i] = rand(gen);
	}
	
	type delta = 0;
	for (size_t i = 0; i != n; ++i){
		delta += a[i] - b[i];
	}
	type abs_delta = std::abs(delta);
	std::cout << a << "\n" << b << "\ndelta = " << abs_delta << "\n";

	size_t step = 0;
	do{
		++step;
		type delta_2 = delta, abs_delta_2 = abs_delta;
		size_t i0, j0;
		for (size_t i = 0; i != n; ++i){
			for (size_t j = 0; j != n; ++j){
				type tmp = a[i] - b[j], tmp_delta = delta - tmp*2, abs_tmp_delta = std::abs(tmp_delta);
				if (abs_tmp_delta < abs_delta_2){
					delta_2 = tmp_delta;
					abs_delta_2 = abs_tmp_delta;
					i0 = i;
					j0 = j;
				}
			}
		}
		if (abs_delta_2 < abs_delta){
			std::swap(a[i0], b[j0]);
			delta = delta_2;
			abs_delta = abs_delta_2;

			std::cout << "\nstep " << step << ": swap(" << i0 << ", " << j0 << ")\n" << a << "\n" << b << "\ndelta = " << abs_delta << "\n";
		}
		else{
			break;
		}
	} while (true);
	
	return 0;
}