575. Distribute Candies

Given an integer array with even length, where different numbers in this array represent different kinds of candies. Each number means one candy of the corresponding kind. You need to distribute these candies equally in number to brother and sister. Return the maximum number of kinds of candies the sister could gain.

Example 1:

Input: candies = [1,1,2,2,3,3]Output: 3Explanation:There are three different kinds of candies (1, 2 and 3), and two candies for each kind.Optimal distribution: The sister has candies [1,2,3] and the brother has candies [1,2,3], too. The sister has three different kinds of candies. 

Example 2:

Input: candies = [1,1,2,3]Output: 2Explanation: For example, the sister has candies [2,3] and the brother has candies [1,1]. The sister has two different kinds of candies, the brother has only one kind of candies. 

Note:

1. The length of the given array is in range [2, 10,000], and will be even.
2. The number in given array is in range [-100,000, 100,000].

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我的解答：

class Solution {public:    int distributeCandies(vector<int>& candies) {        set<int> st(candies.begin(), candies.end());        if(st.size() < candies.size() / 2){            return st.size();        }else{            return candies.size() / 2;        }    }};

在STL中，set是以红黑树（RB-Tree）作为底层数据结构的。set可以在时间复杂度为O（logN）的情况下插入，删除和查找数据。
因此时间复杂度为O(NlogN)

leetcode上的解答：

The idea is to use biset as hash table instead of unordered_set.int distributeCandies(vector<int>& candies) {        bitset<200001> hash;        int count = 0;        for (int i : candies) {            if (!hash.test(i+100000)) {               count++;               hash.set(i+100000);            }        }        int n = candies.size();        return min(count, n/2);    }

时间复杂度应该为O（N）