formula for the number of sums given an array of numbers code example
Example: find pair in unsorted array which gives sum x
// C++ program to check if given array
// has 2 elements whose sum is equal
// to the given value
using namespace std;
// Function to check if array has 2 elements
// whose sum is equal to the given value
bool hasArrayTwoCandidates(int A[], int arr_size,
int sum)
{
int l, r;
/* Sort the elements */
sort(A, A + arr_size);
/* Now look for the two candidates in
the sorted array*/
l = 0;
r = arr_size - 1;
while (l < r) {
if (A[l] + A[r] == sum)
return 1;
else if (A[l] + A[r] < sum)
l++;
else // A[i] + A[j] > sum
r--;
}
return 0;
}
/* Driver program to test above function */
int main()
{
int A[] = { 1, 4, 45, 6, 10, -8 };
int n = 16;
int arr_size = sizeof(A) / sizeof(A[0]);
// Function calling
if (hasArrayTwoCandidates(A, arr_size, n))
cout << "Array has two elements with given sum";
else
cout << "Array doesn't have two elements with given sum";
return 0;
}