[leetcode] 170. Two Sum III - Data structure design 解题报告
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题目链接:https://leetcode.com/problems/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) -> truefind(7) -> false
思路: 用hash表将元素都保存起来,然后查找的时候遍历hash表, 看当前元素与要查找的元素是否存在hash表中.
本题一个主要的问题就是有可能有重复元素, 即如果要查找的值如6, 可能由3+3构成, 这样如果你只有一个3是无法构成6的, 因此要对元素的个数进行记录并判断.
代码如下:
class TwoSum {public: // Add the number to an internal data structure.void add(int number) { hash[number]++;} // Find if there exists any pair of numbers which sum is equal to the value.bool find(int value) { for(auto val: hash) { if(value!=2*val.first && hash.count(value-val.first)) return true; if(value==2*val.first && val.second > 1) return true; } return false;}private: unordered_map<int, int> hash;};// Your TwoSum object will be instantiated and called as such:// TwoSum twoSum;// twoSum.add(number);// twoSum.find(value);
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