某日从聊天记录里翻出来的C++代码

gistfile1.cpp

/*没记错的话，应该是从n个元素中选出m个。当时以英文字母a~z加上数字0~9为元素范围，那么n最大是36了。
印象里1对应该元素被输出，0则不输出，然后……然后？？？
不过，三年过去了，完全看不懂了怎么办？！
似乎去掉system("pause")就能在Linux上编译通过了
*/
#include <fstream>
#include <iostream>
using namespace std;
#define getbit(bits, bit_index) ( bits[bit_index / sizeof(char)] & (1<< (bit_index % sizeof(char))) )
#define setzero(bits, bit_index) ( bits[bit_index / sizeof(char)] &= ~(1<< (bit_index % sizeof(char))) )
#define setone(bits, bit_index) (  bits[bit_index / sizeof(char)] |= (1<< (bit_index % sizeof(char))) )
#define min(a,b) ((a) < (b) ? a:b)
#define max(a,b) ((a) < (b) ? b:a)
template <typename T>
class ListAll{
public :
	ListAll(){}
	~ListAll(){if (bits == 0) delete[] bits;}
	void set_vec(T v[], int n){vec = v; this->n = n;}
	int list(int m);
private:
	void print_one();
	char* bits;
	T* vec; 
	int n;
	int m;
	
	ofstream fout ;
};
template <typename T>
void ListAll<T>::print_one(){
	int c = 0;
	for(int i = 0; i < n, c < m; i++){
		if(getbit(bits, i) == 1){
			fout << vec[i];
			c++;
		}
	}
	fout<<endl;
}
template <typename T>
int ListAll<T>::list(int m){
	int lastOne, lastZero, lastZeroBF;
	int ones, counter = 0;
	this->m = m;
	fout.open("out.txt");
	bits = new char[n / sizeof(char) +1];
	for(int i = 0; i < m; i++) setone(bits,i);
	for(int i = m; i < n; i++) setzero(bits,i);
	lastOne = 0;
	lastZero = m;
	ones = 0;
	while(true){
		print_one();
		counter ++;
		if(counter % 100 == 0)
			cout<<"已输出"<<counter<<endl;
		//找最右边的0（右边至少1个1）
		ones = 0;
		//if(lastZero > lastOne)
		for(lastZeroBF = lastOne; lastZeroBF < n && getbit(bits,lastZeroBF) != 0; lastZeroBF ++, ones ++);
		if( n <= lastZeroBF) break;
		setone(bits, lastZeroBF);
		ones --;
		for(int i = 0; i < ones; i++) setone(bits, i);
		for(int i = ones; i < lastZeroBF; i++) setzero(bits,i);
		if(ones > 0){
			lastOne = 0;
			lastZero = ones;
		}else{
			lastOne = lastZeroBF;
			lastZero = 0;
		}		
	}
//	fout.flush();
	fout.close();
	delete[] bits;
	bits =0;
	return counter;
}
int main(void)
{
	char v[] = "abcdefghijklmnopqrstuvwxyz1234567890";
	int m,n;
	int c;
	ListAll<char> lall;
	while(true){
		do{
			cout<<"请输入n"<<endl;
			cin>>n;
		}while(n < 1 || 36 <n);
		do{
			cout<<"请输入m"<<endl;
			cin>>m;
		}while(m < 1 || m >n);
		
		lall.set_vec(v,n);
		c = lall.list(m);
		cout << "total size " << c<<endl;
		system("pause");
		cout<<"输入1继续，其它退出"<<endl;
		cin>>c;
		if(c != 1)
			break;
	}
	return 0;
}