Sliding Window Maximum

Desicription

Given an array 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:

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Input: nums = [1,3,-1,-3,5,3,6,7], and 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

Note:

You may assume k is always valid, 1 ≤ k ≤ input array’s size for non-empty array.

Follow up:

Could you solve it in linear time?

Solution

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