# 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.

Example 1:

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

Example 2:

``````add(3); add(1); add(2);
find(3) -> true
find(6) -> false
``````

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

``````class TwoSum {
public:
s.insert(number);
}
bool find(int value) {
for (auto a : s) {
int cnt = a == value - a ? 1 : 0;
if (s.count(value - a) > cnt) {
return true;
}
}
return false;
}
private:
unordered_multiset<int> s;
};
``````

Github 同步地址：

https://github.com/grandyang/leetcode/issues/170

Two Sum

Unique Word Abbreviation

Two Sum IV - Input is a BST

https://leetcode.com/problems/two-sum-iii-data-structure-design/

https://leetcode.com/problems/two-sum-iii-data-structure-design/discuss/52015/Beats-100-Java-Code