Given an unsorted array of n integers, find a pair of integers whose sum = k

SumPairOfIntegers.java

//Method 1 : Time = O(n), Space = O(1)
public List<Pair<Integer, Integer>> getPairsOfIntegers( int[] numbers, int sum ){
  List<Pair<Integer,Integer>> results = new ArrayList<>();
  int[] sortedNumbers = doRadixSort( numbers );
  int left = 0;
  int right = sortedNumbers.length - 1;
  while( left < right ){
    int currentSum = sortedNumbers[ left ] + sortedNumbers[ right ];
    if (  currentSum == sum ){
      results.add( new Pair<Integer,Integer>( sortedNumbers[ left ], sortedNumbers[ right ] );
    } else if ( currentSum < sum ){
      left++;  
    } else if ( currentSum > sum ){
      right --;
    }
  }
  return results;
}

//Method 2 : Time = O(n), Space = O(n)

public List<Pair<Integer, Integer>> PairOfIntegers2( int[] numbers, int sum ){
    List<Pair<Integer,Integer>> results = new ArrayList<>();
    Map<Integer, Integer> map = new HashMap<>();
    
    for( int i = 0; i< numbers.length; i++ ){
      int current = numbers[i];
      Integer difference = sum - current;
      if( map.containsKey( current ){
        results.add( new Pair<Integer, Integer>( current, difference );
      } else{
        map.put( difference, current );
      }
    }
    return results;
}