"partition"和“stable_partition”的思考

"partition"和“stable_partition”设计的目的是根据一个谓词而把容器分为两部分。可是他们具体的区别在哪里呢？下面我们来验证一下。

void elimDups(vector<string> &words)
{
    sort(words.begin(), words.end());
    auto it = unique(words.begin(),words.end());
    words.erase(it, words.end());
    for(auto &a : words) cout << a << " ";
    cout << endl;
}
void bigies_partition(vector<string> &words, std::size_t sz)
{
    elimDups(words);
    auto pivot = partition(words.begin(),words.end(),
                           [sz](const string &a){return a.size() < sz;});
    for(auto a = words.begin(); a != pivot; ++a){
        cout << *a << " ";
    }
}
void bigies_stable_partition(vector<string> &words, std::size_t sz)
{
    elimDups(words);
    auto pivot = stable_partition(words.begin(),words.end(),
                           [sz](const string &a){return a.size() < sz;});
    for(auto a = words.begin(); a != pivot; ++a){
        cout << *a << " ";
    }
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    vector<string> v{"aa", "c", "ffff","bb","dddddd","eee","aaa","bbb"};


    vector<string> v1(v);
    cout << "partition:" << endl;
    bigies_partition(v1,3);
    cout << endl;

    vector<string> v2(v);
    cout << "stable_partition:" << endl;
    bigies_stable_partition(v2,3);
    cout << endl;

    return a.exec();
}

output:

partition
aa aaa bb bbb c dddddd eee ffff
aa c bb
stable_partition
aa aaa bb bbb c dddddd eee ffff
aa bb c

可以发现，stable_partition除了根据谓词把容器划分为两部分，还可以保持容器原有元素的顺序。