LeetCode 170. 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,

add(1); add(3); add(5);

find(4) -> true

find(7) -> false

思路：

1. TwoSum，首先就是用hash，add()时把每个数存入hash，统计出现的次数作为value；find()时，遍历hash，查找target-hash中每一个key，如果查找的数不等于target-key,只要存在即可；如果查找的数等于target-key,则查找的数的出现频率大于等于2即可！

class TwoSum {
public:
void add(int number) {
++m[number];
}
bool find(int value) {
for(auto&mm:m){
if(value-mm.first==mm.first&&mm.second>1) return true;
if(value-mm.first!=mm.first&&m.count(value-mm.first)) return true;
}
return false;
}
private:
unordered_map<int,int> m;