Question

Using simple and basic C++ (do not use #include <algorithm>), write two functions (one for a sorted arrays of integers and one for an unsorted array of integers) to check if any pair of elements in an array of integers add up to 20 and print all the pairs that do

Answer 1

#include <iostream>
using namespace std;

//brute force method where we check all the combinations and see if their sum is 20
void print_pairs_forunsorted(int a[],int n)
{
   int i,j;
cout<<"\nPrinting pairs for unsorted array";
   for(i=0;i<n;i++)
   {
for(j=i+1;j<n;j++)
{
if(a[i]+a[j]==20)
{
cout<<"\n("<<a[i]<<","<<a[j]<<")";
}
}
   }

}

//for sorted we have two pointers one to the beginning l and one to ending r

//if a[l]+a[r] is less than 20 then we need to choose element greater than a[l] so we increment l

//if a[l]+a[r] is greaterthan 20 then we need to choose element lessthan a[r] so we decrementl
void print_pairs_forsorted(int a[],int n)
{
int l = 0;
int r = n - 1;
cout<<"\nPrinting pairs for sorted array";
while (l < r)
{
if(a[l]+a[r]== 20)
{
cout<<"\n("<<a[l]<<","<<a[r]<<")";
l++;
r--;
}
else if(a[l]+a[r]< 20)
l++;
else if(a[l]+a[r]>20)
r--;
}
}
int main()
{
   int a[] = {1, 2, 3, 17, 18, 20};
   int b[] = {11, 2, 9, 17, 18, 3};
print_pairs_forunsorted(b,6);
print_pairs_forsorted(a,6);
   return 0;
}