Question

Using C++ write a program to find the kth smallest element in the concatenation of two vectors A and B, given that both vectors are sorted in decreasing order. You can assume 1 ≤ k ≤ A.size() + B.size(). The function declaration is given below.

int findKthSmallest(vector A, vector B, int k);

For example, for A = [4, 2, 1] and B = [7, 5, 2, -3], the 2nd smallest element in the concatenation of A and B is 1.

Your job is to implement a findKthSmallest as a single function as described above.

Answer 1

Answer:

#include <iostream>
#include<vector>
#include<bits/stdc++.h>
using namespace std;

int findKthSmallest(vector <int> A,vector <int> B, int k)
{
int a_size,b_size;
vector <int> C;
a_size =A.size()-1;
b_size = B.size()-1;
while((a_size>=0)&&(b_size>=0))
{
if(A[a_size] < B[b_size])
{
C.push_back(A[a_size]);
a_size = a_size -1;
}
else
{
C.push_back(B[b_size]);
b_size--;
}
}
  
if(a_size<0){
while(b_size >=0)
{
C.push_back(B[b_size]);
b_size= b_size-1;
}
}
else
{
while(a_size >=0)
{
C.push_back(A[a_size]);
a_size= a_size-1;
}
}

return C[k-1];
}

int main()
{
vector <int> A;
vector <int> B;
int i,res,k;
for(i=0;i<3;i++)
{
A.push_back(4);
A.push_back(2);
A.push_back(1);
}
  
for(i=0;i<4;i++)
{
B.push_back(7);
B.push_back(5);
B.push_back(2);
B.push_back(-3);
}
cout<<"Enter k value for calculating smallest element merging array :";
cin>>k;
res = findKthSmallest(A,B,k);
cout<<k<<" th smallest element is :"<<res;
return 0;
}

we need to traverse the array from the last index because array is in descending order.
Always array last index starts from size -1.
we need to declare a new vector in order to store the merging result.
If the element in the first array is lesser than the second array then we need to store first array
value in the new array.Otherwise store the element of second array.
we need to decrement the index value of the array from which you have appended the element into result array.

we need to insert all the elements in sorted order in the resultant vector.

Array indexes starts from zero .so we need to extract the K-1th index  if we want to access kth element.