two pointer in c++
int i = 0;
// represents second pointer
int j = N - 1;
while (i < j) {
// If we find a pair
if (A[i] + A[j] == X)
return 1;
// If sum of elements at current
// pointers is less, we move towards
// higher values by doing i++
else if (A[i] + A[j] < X)
i++;
// If sum of elements at current
// pointers is more, we move towards
// lower values by doing j--
else
j--;
}