one simple algorithm:
0. get the inputs from console
1. sort the input array as sortedInput
2. set lowestDiff to maximum integer value
3. set resultArray to empty array
4. for i = 1 to length of sortedInput-1
    4a. delta = absolute value (sortedInput[i] - sortedInput[i-1])
    4b. if delta < lowestDiff, then
        -> lowestDiff = delta
        -> clear resultArray (remove all elements from array)
        -> add to resultArray sortedInpit[i-1], and then sortedInput[i]
4c. Else, if delta == lowestDiff, then
        -> add to resultArray sortedInpit[i-1], and then sortedInput[i]
5. print resultArray as space-separated integer on single line.