滑动窗口的最大值

class Solution {
public:
    vector<int> maxInWindows(const vector<int>& num, unsigned int size)
    {
        vector<int> res;
        if(num.empty() || size<=0)
            return res;
        int i=0;
        for(; i<size; ++i)
        {
            if(index.empty())
            {
                index.push_back(i);
            }
            else
            {
                if(num[i] >= num[index.back()])
                    index.pop_back();
                    index.push_back(i);
                
            }
        }
        
        for(; i<=num.size(); ++i)
        {
            res.push_back(num[index.front()]);
            while(!index.empty() && num[i]>=num[index.back()])
                  index.pop_back();
            index.push_back(i);
            while(!index.empty() && index.front()<=(i-size))
                   index.pop_front();
            
        }
        return res;
    }
private:
    deque<int> index;
};