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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
思路：思路跟two sum差不多，用hashmap存读到的数，value存个数。find只要遍历map然后检查是不是有被减数，如果被减数等于减数，检查个数即可。
public class TwoSum { Map<Integer,Integer> res=new HashMap<Integer,Integer>(); // Add the number to an internal data structure. public void add(int number) { if(res.containsKey(number)) { res.put(number,res.get(number)+1); } else { res.put(number,1); } } // Find if there exists any pair of numbers which sum is equal to the value. public boolean find(int value) { if(res.isEmpty()) { return false; } for(int number:res.keySet()) { if(res.containsKey(value-number)) { if(value-number==number) { if(res.get(number)>=2) { return true; } } else { return true; } } } return false; } } // Your TwoSum object will be instantiated and called as such: // TwoSum twoSum = new TwoSum(); // twoSum.add(number); // twoSum.find(value);
170. Two Sum III - Data structure design
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原文地址：http://www.cnblogs.com/Machelsky/p/5892263.html
