480 Sliding Window Median 滑动窗口中位数

详见：https://leetcode.com/problems/sliding-window-median/description/

C++：

class Solution {
public:
    vector<double> medianSlidingWindow(vector<int>& nums, int k)
    {
        vector<double> res;
        multiset<double> ms(nums.begin(), nums.begin() + k);
        auto mid = next(ms.begin(), k /  2);
        for (int i = k; ; ++i)
        {
            res.push_back((*mid + *prev(mid,  1 - k % 2)) / 2);
            if (i == nums.size())
            {
                return res;
            }
            ms.insert(nums[i]);
            if (nums[i] < *mid)
            {
                --mid;
            }
            if (nums[i - k] <= *mid)
            {
                ++mid;
            }
            ms.erase(ms.lower_bound(nums[i - k]));
        }
    }
};

参考：http://www.cnblogs.com/grandyang/p/6620334.html