Two Sum III - Data structure design

Design and implement a TwoSum class. It should support the following operations: add and find.

  • add - Add the number to an internal data structure.
  • find - Find if there exists any pair of numbers which sum is equal to the value.

For example,

  1. add(1); add(3); add(5);
  2. find(4) -> true
  3. find(7) -> false

Solution:

  1. public class TwoSum {
  2.   private HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
  4.   public void add(int number) {
  5.     if (map.containsKey(number)) {
  6.       map.put(number, map.get(number) + 1);
  7.     } else {
  8.       map.put(number, 1);
  9.     }
  10.   }
  12.   public boolean find(int value) {
  13.     for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
  14.       int key = entry.getKey();
  15.       int idx = entry.getValue();
  17.       int val = value - key;
  19.       if (key != val && map.containsKey(val)) {
  20.         return true;
  21.       }
  23.       if (key == val && map.get(key) > 1) {
  24.         return true;
  25.       }
  26.     }
  28.     return false;
  29.   }
  30. }