Two elements whose sum is closest to zero | GeeksforGeeks

An Array of integers is given, both +ve and -ve. You need to find the two elements such that their sum is closest to zero.

METHOD 2 (Use Sorting) 
1) Sort all the elements of the input array.
2) Use two index variables l and r to traverse from left and right ends respectively. Initialize l as 0 and r as n-1.
3) sum = a[l] + a[r]
4) If sum is -ve, then l++
5) If sum is +ve, then r–
6) Keep track of abs min sum.
7) Repeat steps 3, 4, 5 and 6 while l < r

void minAbsSumPair(int arr[], int n)

{

  // Variables to keep track of current sum and minimum sum

  int sum, min_sum = INT_MAX;

  // left and right index variables

  int l = 0, r = n-1;

  // variable to keep track of the left and right pair for min_sum

  int min_l = l, min_r = n-1;

  /* Array should have at least two elements*/

  if(n < 2)

  {

    printf("Invalid Input");

    return;

  }

  /* Sort the elements */

  quickSort(arr, l, r);

  while(l < r)

  {

    sum = arr[l] + arr[r];

    /*If abs(sum) is less then update the result items*/

    if(abs(sum) < abs(min_sum))

    {

      min_sum = sum;

      min_l = l;

      min_r = r;

    }

    if(sum < 0)

      l++;

    else

      r--;

  }

}

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