数据结构与算法分析 3.4&3.5 — 链表的交与并算法

代码：

#include <list>

template<typename ElementType>
list<ElementType> Intersect(const list<ElementType> &list_1, const list<ElementType> &list_2)
{
    list<ElementType> result;
    auto leftPos = list_1.begin( );
    auto rightPos = list_2.begin( );

    while (leftPos != list_1.end() && rightPos != list_2.end())
    {
        if (*leftPos > *rightPos)
            rightPos++;
        else
        if (*leftPos < *rightPos)
            leftPos++;
        else
        {
            result.push_back(*leftPos);++leftPos, ++rightPos;
        }
    }
    return result;
}

template<typename ElementType>
list<ElementType> Union(const list<ElementType> &list_1, const list<ElementType> &list_2 )
{
    list<ElementType> result;
    auto leftPos = list_1.cbegin( );
    auto rightPos = list_2.cbegin( );

    while (leftPos != list_1.end() && rightPos != list_2.end())
    {
        if (*leftPos < *rightPos)
            result.push_back(*leftPos), ++leftPos;
        else
        if (*leftPos > *rightPos)
            result.push_back(*rightPos), ++rightPos;
        else
        {
            result.push_back(*leftPos);
            ++leftPos, ++rightPos;
        }
    }
    while (leftPos != list_1.end( ))
        result.push_back(*leftPos), leftPos++;
    while (rightPos != list_2.end( ))
        result.push_back(*rightPos), rightPos++;
    return result;
}