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] << " ";
}

Input

{{ 2,4}, { 3,5,7 }, { 1, 10, 11, 12 }}

Output

1 2 3 4 5 7 10 11 12