EPI (Heap) Merge Multiple sorted arrays.

#include <vector>#include <iostream>#include <queue>using namespace std;/*  Write a program that takes an input a set of sorted sequences and compute the union  of these sequences as a sorted sequence.  For example:  [3, 5, 7], [0, 6, 8], [0, 6, 28], then the output is [0, 0, 3, 5, 6, 6, 7, 28]*//*  This problem can further be divided into two.   1: There are only two sorted sets.  2: The number of input sets are more than two.*/// Time complexity: O(N), Space O(N)vector<int> mergeTwoSets(vector<int>& set_1, vector<int>& set_2) {  int m = set_1.size();  if(m == 0) return set_2;  int n = set_2.size();  if(n == 0) return set_1;  vector<int> res;  int i = 0, j = 0;  while(i < m && j < n) {    if(set_1[i] <= set_2[j]) {      res.push_back(set_1[i++]);    } else {      res.push_back(set_2[j++]);    }  }  while(i < m) {    res.push_back(set_1[i++]);  }  while(j < n) {    res.push_back(set_2[j++]);  }  return res;}void printVector(vector<int>& res) {  for(int i = 0; i < res.size(); ++i) {    cout << res[i] << endl;  }}// Identical with merging multiple sorted lists. Time complexity: NlgK (K is the number of input size). Space lgKvector<int> mergeMultiSets(const vector< vector<int> >& sets) {  struct IteratorStartAndEnd {    bool operator < (const IteratorStartAndEnd& that) const {      return *start > *that.start;    }    vector<int>::const_iterator start;    vector<int>::const_iterator end;  };  priority_queue< IteratorStartAndEnd, vector<IteratorStartAndEnd> > minHeap;  for(const vector<int>& sorted_array : sets) {    if(!sorted_array.empty())    minHeap.push(IteratorStartAndEnd{sorted_array.cbegin(), sorted_array.cend()});  }  vector<int> res;  while(!minHeap.empty()) {    auto smallest_array = minHeap.top();    minHeap.pop();    if(smallest_array.start  != smallest_array.end) {      res.push_back(*smallest_array.start);      minHeap.push(IteratorStartAndEnd{next(smallest_array.start), smallest_array.end});    }  }  return res;}int main(void) {  vector<int> set_1{0, 15};  vector<int> set_2{2, 3, 10, 12};  vector<int> set_3{2, 3, 9, 14};//  vector<int> res = mergeTwoSets(set_1, set_2);  //printVector(res);  vector< vector<int> > multisets;  multisets.push_back(set_1);  multisets.push_back(set_2);  multisets.push_back(set_3);  vector<int> res_1 = mergeMultiSets(multisets);  printVector(res_1);}