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C++ 模板实现败者树，进行多路归并

2024-07-27 18:52:13   212人阅读

项目需要实现一个败者树，今天研究了一下，附上实现代码。

几点说明：

1. 败者树思想及实现参考这里：http://www.cnblogs.com/benjamin-t/p/3325401.html

2. 多路归并中的“多路”的容器使用的是C语言数组 + 数组长度的实现（即

const ContainerType* ways, size_t num

），而没有用STL中的容器，这是因为项目需要如此，日后再改成STL容器；

3. _losers 存储下标，用的是 int 类型，还需要修改。程序中其他下标类型都是 size_t，但是这个 _losers 存的下标需要使用 -1 表示无效。

4. Foo 还不能用在 std::copy上，待修正；

5. 使用了 FooContainer<Foo> 类型以后，输出的时候不能直接输出，必须定义一个变量再输出，不知道为什么：

            //std::cout << data[i][j] << ", ";  
            Foo foo = data[i][j];
            std::cout << foo << ", ";

6. 把 const 变量作为 non-type template parameter 时，必须把该 const 变量定义在全局，并且加 extern，原因见这里：http://stackoverflow.com/questions/9183485/const-variable-as-non-type-template-parameter-variable-cannot-appear-in-a-const

7. 代码放在Github上：https://github.com/qinpeixi/code-pieces

8. 一个专业级的实现在这里：https://github.com/MITRECND/snugglefish

 

代码如下：

#include <iostream>#include <vector>#include <iterator>#include <string>#include <sstream>#include <cstdlib>#include <cassert>class Foo {public:    Foo() {}    explicit Foo(int v): _v(v) {}    Foo(const Foo& foo) { _v = foo._v; }    int value() const { return _v; }    Foo& operator=(const Foo& foo) { _v = foo._v; return *this; }    bool operator==(const Foo& foo) { return _v == foo._v; }private:    int _v;};std::ostream& operator<<(std::ostream& os, Foo& foo) {    return os << foo.value();}extern const Foo FOO_MAX(INT_MAX);namespace  std {template<>class less<Foo> : std::binary_function<Foo, Foo, bool>{public:    bool operator() (const Foo& x, const Foo& y) const {        return x.value() < y.value();    }};} // namespace stdtemplate<class ValueType>class FooContainer{public:    ValueType operator[](size_t idx) const { return _container[idx]; }    size_t size() const { return _container.size(); }    void push_back(const ValueType& value) {        _container.push_back(value);    }private:    std::vector<ValueType> _container;};template< class ValueType,          class ContainerType,          const ValueType& max_value,          class Compare = std::less<ValueType> >class LoserTree{public:    ~LoserTree() {        delete[] _indexes;        delete[] _losers;        delete[] _data;    }    LoserTree(const ContainerType* ways, size_t num) :        _num(num), _ways(ways), _indexes(new size_t[_num]),        _data(new ValueType[_num]), _losers(new int[_num])    {        std::fill(_indexes, _indexes + _num, 0);        std::fill(_losers, _losers + _num, -1);        for (int way_idx = _num-1; way_idx >= 0; --way_idx) {            if (_indexes[way_idx] == _ways[way_idx].size()) {                _data[way_idx] = max_value;            } else {                _data[way_idx] = _ways[way_idx][_indexes[way_idx]];            }            adjust(way_idx);        }    }    bool extract_one(ValueType& v) {        int way_idx = _losers[0];        if (_data[way_idx] == max_value)            return false;        v = _data[way_idx];        if (++_indexes[way_idx] == _ways[way_idx].size()) {            _data[way_idx] = max_value;        } else {            _data[way_idx] = _ways[way_idx][_indexes[way_idx]];        }        adjust(way_idx);        return true;    }private:    size_t _num;    const ContainerType* _ways;    size_t* _indexes;    ValueType* _data;    int* _losers;    void adjust(int way_idx) {        using std::swap;        int loser_idx = (way_idx + _num) / 2;        while (loser_idx != 0 && way_idx != -1) {            if (_losers[loser_idx] == -1 || !Compare()(_data[way_idx],  _data[_losers[loser_idx]]))                swap(way_idx,_losers[loser_idx]);            loser_idx /= 2;        }        _losers[0] = way_idx;    }};/* * input format: * 1 10 100 1000 * 2 20 200 2000 * 3 30 300 * 4 40 400 4000 40000 */std::vector<std::vector<int> > get_input(){    std::vector<std::vector<int> > data;    std::string line;    while (std::getline(std::cin, line)) {        std::vector<int> tmp_data;        std::istringstream iss(line);        std::copy(std::istream_iterator<int>(iss), std::istream_iterator<int>(), std::back_inserter(tmp_data));        data.push_back(tmp_data);    }    for (size_t i = 0; i < data.size(); ++i) {        std::copy(data[i].begin(), data[i].end(), std::ostream_iterator<int>(std::cout, ", "));        std::cout << std::endl;    }    return data;}template<class ValueType, class ContainerType>std::vector<ContainerType> generate_data(){    const int way_num = 20;    std::vector<ContainerType> data(way_num);    for (int num = 0; num < 10/*100000*/; ++num) {        data[rand() % way_num].push_back(ValueType(num));    }    return data;}void test_foo(){    std::vector<FooContainer<Foo> > data = http://www.mamicode.com/generate_data >();    /*    for (size_t i = 0; i < data.size(); ++i) {        for (size_t j = 0; j < data[i].size(); ++j) {            //std::cout << data[i][j] << ", ";            Foo foo = data[i][j];            std::cout << foo << ", ";        }        std::cout << std::endl;    }    */    LoserTree<Foo, FooContainer<Foo>, FOO_MAX> lt(data.data(), data.size());    Foo v;    Foo correct_res(0);    while(lt.extract_one(v)) {        //assert(v == correct_res);        //correct_res = Foo(correct_res.value()+1);        std::cout << v.value() << ", ";    }    std::cout << std::endl;}extern const int int_max = INT_MAX;void test(){    std::vector<std::vector<int> > data = http://www.mamicode.com/generate_data<int ,std::vector<int> >();    LoserTree<int, std::vector<int>, int_max> lt(data.data(), data.size());    int v;    int correct_res(0);    while (lt.extract_one(v)) {        assert(v == correct_res++);        std::cout << v << ", ";    }    std::cout << std::endl;}int main(){    test_foo();    test();    return 0;}

 

C++ 模板实现败者树，进行多路归并


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