[LeetCode] 170. Two Sum III - Data structure design 两数之和之三 - 数据结构设计

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

Two Sum题的拓展，设计一个数据结构，实现添加数字和找目标数字的功能。用HashMap来存数字和查找。

Java:

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public class TwoSum {     private HashMap<Integer, Integer> elements = new HashMap<Integer, Integer>();        public void add(int number) {         if (elements.containsKey(number)) {             elements.put(number, elements.get(number) + 1);         } else {             elements.put(number, 1);         }     }        public boolean find(int value) {         for (Integer i : elements.keySet()) {             int target = value - i;             if (elements.containsKey(target)) {                 if (i == target && elements.get(target) < 2) {                     continue;                 }                 return true;             }         }         return false;     } }

 Python:

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class TwoSum(object):       def __init__(self):         self.dic = {}       def add(self, number):         if number not in self.dic:             self.dic[number] = 1         else:             self.dic[number] += 1       def find(self, value):         dic = self.dic         for num in dic:             if value - num in dic and (value - num != num or dic[num] > 1):                 return True         return False

　　

Python:

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class TwoSum(object):       def __init__(self):         self.lookup = defaultdict(int)               def add(self, number):         self.lookup[number] += 1       def find(self, value):         for key in self.lookup:             num = value - key             if num in self.lookup and (num != key or self.lookup[key] > 1):                 return True         return False

 

C++:

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class TwoSum { public:     void add(int number) {         ++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; };

　　

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