Merge k sorted arrays of different sizes in C++

Suppose we have different k sorted arrays. We have to merge these arrays and display the sorted result.

So, if the input is like k = 3 and arrays are {2, 4},{3, 5, 7},{1, 10, 11, 12} , then the output will be 1 2 3 4 5 7 10 11 12

To solve this, we will follow these steps −

define one type of pair with first element is an integer and second element is another pair of integers, name it as ppi.
Define an array op
define one priority queue q
for initialize i := 0, when i < size of arr, update (increase i by 1), do −
- insert (arr[i, 0], {i, 0} )into q
while q is not empty, do −
- current_element := top element of q
- delete element from q
- i := second element from current_element
- j := third element from current_element
- insert first element of current_element at the end of op
- if j + 1 < size of arr[i], then &minus
  - insert (arr[i, j+1], {i, j+1} )into q
return op

Example

Let us see the following implementation to get better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
#define ppi pair<int,pair<int,int>>
vector<int> merge(vector<vector<int> > arr){
   vector<int> op;
   priority_queue<ppi, vector<ppi>, greater<ppi> > queue;
   for (int i = 0; i < arr.size(); i++)
   queue.push({ arr[i][0], { i, 0 } });
   while (queue.empty() == false) {
      ppi current_element = queue.top();
      queue.pop();
      int i = current_element.second.first;
      int j = current_element.second.second;
      op.push_back(current_element.first);
      if (j + 1 < arr[i].size())
      queue.push({ arr[i][j + 1], { i, j + 1 } });
   }
   return op;
}
int main(){
   vector<vector<int> > arr{ { 2,4}, { 3,5,7 }, { 1, 10, 11, 12 } };
   vector<int> output = merge(arr);
   for(int i = 0; i<output.size(); i++)
   cout << output[i] << " ";
}