数据流的中位数

一. 数组

class MedianFinder {
public:
    MedianFinder() {
        n = 0;
    }
    void addNum(int num) {
        n++;
        nums.push_back(num);
        int index = n - 1;
        for(int i=index;i>0;i--)
            if(nums[i]<nums[i-1]) swap(nums[i],nums[i-1]);
    }
    double findMedian() {
        if(n%2==0) return (nums[n/2]+nums[n/2-1])*1.0/2;
        else return nums[n/2];
    }
    private:
        vector<int> nums;
        int n;
};

二. 双优先队列（大根堆小根堆）

class MedianFinder {
public:
    priority_queue<int, vector<int>, less<int>> queMin;//大根堆存储更小值
    priority_queue<int, vector<int>, greater<int>> queMax;//小根堆存储更大值

    MedianFinder() {}
    void addNum(int num) { 
        if (queMin.empty() || num <= queMin.top()) {//优先放大根堆
            queMin.push(num);
            if (queMax.size() + 1 < queMin.size()) {//个数差距为2，进行平衡
                queMax.push(queMin.top());
                queMin.pop();
            }
        } else {
            queMax.push(num);
            if (queMax.size() > queMin.size()) {//进行平衡
                queMin.push(queMax.top());
                queMax.pop();
            }
        }
    }

    double findMedian() {
        if (queMin.size() > queMax.size())//总个数为奇数
            return queMin.top();//返回小根堆顶部
        return (queMin.top() + queMax.top()) / 2.0;
    }
};