Find a pair of elements from an array whose sum equals a given number

Question

Given array of n integers and given a number X, find all the unique pairs of elements (a,b), whose summation is equal to X.

The following is my solution, it is O(nLo

Answer 1

# Let arr be the given array.
# And K be the give sum


for i=0 to arr.length - 1 do
  # key is the element and value is its index.
  hash(arr[i]) = i  
end-for

for i=0 to arr.length - 1 do
  # if K-th element exists and it's different then we found a pair
  if hash(K - arr[i]) != i  
    print "pair i , hash(K - arr[i]) has sum K"
  end-if
end-for