Merge Sorted Stream | tech::interview


Merge Sorted Stream | tech::interview
输入为一个Iterator数组,这些Iterator分别取出来的数都是已排序的,设计并实现一个MergeIterator类,merge这些sorted iterator。
你的MergeIterator类需要包含has_next和get_next方法。
注意,Iterator也只包含has_next和get_next方法。
G家的onsite题,实际上就是多路归并,用一个heap就可以搞定,注意类的细节设计即可。
看过一个面经,面试者跟面试官说Iterator的接口需要有个peek()函数(即只看,不move),实际上是可以不需要的。
MergeIterator(vector<Iterator> streams) {
for(auto& pi : streams) {
if(!pi.has_next()) continue;
_heap.emplace(pi.get_next(), _streams.size());
_streams.push_back(pi);
}
}
int get_next() {
auto ret = _heap.top();
_heap.pop();
if(_streams[ret.second].has_next())
_heap.emplace(_streams[ret.second].get_next(), ret.second);
return ret.first;
}
bool has_next() { return !_heap.empty(); }
private:
using _pair = pair<int,int>;
vector<Iterator> _streams;
priority_queue<_pair,vector<_pair>,function<bool(_pair&,_pair&)>> _heap {
[](_pair& a, _pair& b){return a.first >= b.first;}
};
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