Sliding Window Maximum.cpp

/*
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.

Example 1:
Input: nums = [1,3,-1,-3,5,3,6,7], k = 3
Output: [3,3,5,5,6,7]
Explanation: 
Window position                Max
---------------               -----
[1  3  -1] -3  5  3  6  7       3
 1 [3  -1  -3] 5  3  6  7       3
 1  3 [-1  -3  5] 3  6  7       5
 1  3  -1 [-3  5  3] 6  7       5
 1  3  -1  -3 [5  3  6] 7       6
 1  3  -1  -3  5 [3  6  7]      7

Example 2:
Input: nums = [1], k = 1
Output: [1]

Example 3:
Input: nums = [1,-1], k = 1
Output: [1,-1]

Example 4:
Input: nums = [9,11], k = 2
Output: [11]

Example 5:
Input: nums = [4,-2], k = 2
Output: [4]

Constraints:
1 <= nums.length <= 105
-104 <= nums[i] <= 104
1 <= k <= nums.length
*/

class Solution
{
public:
  vector<int> maxSlidingWindow(vector<int> &nums, int k)
  {
    list<pair<int, int>> window;
    vector<int> ans;

    for (int i = 0; i < nums.size(); ++i)
    {
      auto curr = nums[i];
      while (window.size() && window.front().second <= i - k)
        window.pop_front();
      while (window.size() && window.back().first < curr)
        window.pop_back();
      window.push_back({curr, i});
      if (i >= k - 1)
        ans.push_back(window.front().first);
    }

    return ans;
  }
};