QStringList 去除重复项算法赏析

    QStringList list;
    list<<"2222"<<"xxx"<<"1111"<<"2222"<<"xxxx"<<"1111";
    int n=list.removeDuplicates();

/*!
    \fn int QStringList::removeDuplicates()

    \since  4.5

    This function removes duplicate entries from a list.
    The entries do not have to be sorted. They will retain their
    original order.

    Returns the number of removed entries.
*/
int QtPrivate::QStringList_removeDuplicates(QStringList *that)
{
    int n = that->size();
    int j = 0;
    QSet<QString> seen;
    seen.reserve(n);
    int setSize = 0;
    for (int i = 0; i < n; ++i) {
        const QString &s = that->at(i);
        seen.insert(s);
        if (setSize == seen.size()) // unchanged size => was already seen
            continue;
        ++setSize;
        if (j != i)
            that->swap(i, j);    //将不重复项与重复项交换
        ++j;
    }
    if (n != j)
        that->erase(that->begin() + j, that->end());
    return n - j;
}

list<<"2222"<<"xxx"<<"1111"<<"2222"<<"xxxx"<<"1111";

that->erase(that->begin() + j, that->end());

list<<"2222"<<"xxx"<<"1111"<<"xxxx";