239. Sliding Window Maximum

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239. Sliding Window Maximum

Description

Difficulty: Hard

Related Topics: Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue

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:

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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:

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

Constraints:

  • 1 <= nums.length <= 105
  • -104 <= nums[i] <= 104
  • 1 <= k <= nums.length

Hints/Notes

  • 2023/09/20
  • Monotonic Queue
  • it’s better to record the index
  • 0x3F’s solution(checked)

Solution

Language: C++

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