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,
add(1); add(3); add(5); find(4) -> true find(7) -> false
首先想到用doubly linkedlist 来做， 每次加入的时候维护list 是sorted的， 然后查询的时候左右夹比就行了。 但是这样time out。
所以用hashmap来做。
1 public class TwoSum { 2 HashMap<Integer, Integer> map = new HashMap<Integer, Integer>(); 3 public void add(int number) { 4 if(map.containsKey(number)) map.put(number, map.get(number) + 1); 5 else map.put(number, 1); 6 } 7 8 public boolean find(int value) { 9 for(Integer val : map.keySet()){ 10 if(value == val + val && map.get(val) > 1) return true; 11 if(value != val + val && map.containsKey(value - val)) return true; 12 } 13 return false; 14 } 15 }
Two Sum III - Data structure design
原文：http://www.cnblogs.com/reynold-lei/p/4233864.html