239. Sliding Window Maximum

You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position.

Return the max sliding window.

• Time : O(n)
• Space : O(k)

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        deque<int> dq;
        vector<int> res;
        for(int i = 0; i < nums.size(); i++) {
            if(!dq.empty() and dq.front() == i - k) dq.pop_front();
            while(!dq.empty() and nums[dq.back()] < nums[i]) dq.pop_back();
            dq.push_back(i);
            if(i >= k - 1) res.push_back(nums[dq.front()]);
        }
        return res;
    }
};

• Time : O(n²logn)
• Space : O(k)

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        multiset<int> ms;
        vector<int> res;
        for(int i = 0; i < k - 1; i++) {
            ms.insert(nums[i]);
        }
        for(int i = k - 1; i < nums.size(); i++) {
            ms.insert(nums[i]);
            res.push_back(*ms.rbegin());
            ms.erase(ms.find(nums[i-(k-1)]));
        }
        return res;
    }
};