滑动窗口最大值

https://leetcode-cn.com/problems/sliding-window-maximum/

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        deque<int> q;
        vector<int>  res;
        if(nums.size() ==0 ||k>nums.size()) return res;
        //初始化前第一个窗口
        for (int i = 0; i < k; i++) {
            while (!q.empty()&& nums[i]>nums[q.back()])
            {
                q.pop_back();
            }
            q.push_back(i);
        }
        //初始化前第一个窗口
        res.push_back(nums[q.front()]);
        //开始滑动
        for (int j = k; j < nums.size(); j++) {
            //判断队列中最大值所对应的元素是否在当前窗口里；如果不在当前窗口内就把它移出队列
            if (!q.empty()&&j - q.front() >= k) {
                q.pop_front();
            }
            while (!q.empty()&&nums[j]> nums[q.back()])
            {
                q.pop_back();
            }
            q.push_back(j);
            res.push_back(nums[q.front()]);


        }
        return res;

    }

};