Given a sorted array A[1..n] with n integers, and an integer t, find all pairs (x,y) of elements in A such that x+y is smaller than t. 2. Can we do

Array A[i...n]. t is the given value.
Create a hash of size t assuming t <= n and 1 < t.
Iterate the array to create a hash O(t) (t < n).
The key of the hash should be the value A[i] and value of the hash should be (t - A[i]).

Iterate again over the array again (which is O(t)).
Look up every key in hash matching the value of A[i]. Check if there is an existing key in the hash table which matches value of the A[i].

The hash lookups are constant time. The overall complexity is 2n.