31.位圖bitset

位圖概念

所謂位圖，就是用每一位來存放某種狀態，適用於海量數據，數據無重複的場景。通常是用來判斷某個數據存不存在的

使用方式：

#include <iostream>
#include <bitset>
using namespace std;
int main() {
	bitset<10> bt;
	cout << bt << endl;
	cout <<"size:"<< bt.size() << endl;
	
	bt.set(4);
	cout<<bt.set(3)<<endl;  //設置某一位, 返回值是所操作的bitset對象
	cout << bt.set(3, false) << endl;  //將第三位設置爲0，set的第二個bool類型的參數默認值爲true
	cout << bt.set() << endl;  //設置所有位爲1


	cout<<bt.test(3)<<endl;  //測試某一位

	cout << bt[3] << endl;  //通過重載的運算符[]訪問某一位
	//cout << bt[12] << endl;  //越界操作程序會崩潰
	//cout << bt.at(3)<<endl;  //Vs2019將at方法刪除了，VS2013任然可以用
	//cout << bt.at(12) << endl;  //越界操作程序會崩潰

	cout << bt.reset(3) << endl;
	cout<<bt.reset()<<endl;  //將所有位重置爲0

	cout << bt.flip() << endl;  //所有二進制位取反

	cout << (bt <<= 2) << endl;  //左移兩位

	cout << bt.count() << endl;  //統計位爲1的位數

	cout << bt.to_ulong() << endl;  //將位圖轉換爲unsigned long類型
	cout << bt.to_ullong() << endl;  //將位圖轉換爲unsigned long long類型
	auto s = bt.to_string();
	cout << typeid(s).name() << endl;
	cout << bt.to_string() << endl;  //將位圖轉換爲string類型
	return 0;
}

bitset模擬實現

#include <iostream>
#include <vector>
using namespace std;
//simulation of bitset
template<size_t _N>
class bitSet {
public:
	bitSet() :_bitArray((_N >> 5) + 1), _bitCount(_N) {  //_N/32+1
	}
	void set(size_t pos) {
		if (pos >= _bitCount)
			return;
		_bitArray[pos >> 5] |= (1 << (pos % 32));
	}
#if 0
//C++11
	size_t count() {
		int bitCnttable[256] = {
			0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, 4, 2,
			3, 3, 4, 3, 4, 4, 5, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3,
			3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3,
			4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4,
			3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5,
			6, 6, 7, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4,
			4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5,
			6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 2, 3, 3, 4, 3, 4, 4, 5,
			3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 3,
			4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7, 5, 6,
			6, 7, 6, 7, 7, 8 	};
		size_t size = _bit.size();
		size_t count = 0;
		for (size_t i = 0; i < size; ++i)
		{
			int value = _bit[i];
			int j = 0;
			while (j < sizeof(_bit[0]))
			{
				unsigned char c = value;
				count += bitCntTable[c];
				++j;
				value >>= 8;
			}
		}
		return count;
	}
#else
//vC6.0-C++98
	size_t count() const {
		int size = _bitArray.size();
		size_t _V = 0;
		for (int i = size - 1; 0 <= i; --i) {
			for (size_t eachEle = _bitArray[i]; eachEle != 0; eachEle >>= 4)
				_V += "\0\1\1\2\1\2\2\3\1\2\2\3\2\3\3\4"[eachEle & 0xF];
		}
		return _V;
	}

#endif
private:
	vector<int> _bitArray;
	size_t _bitCount;
};
int main() {
	bitSet<36> bs;
	bs.set(10);
	bs.set(20);
	bs.set(30);
	bs.set(35);
	cout<< bs.count() << endl;
	return 0;
}