239. [LeetCode ]Sliding Window Maximum

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:

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

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---

#include <cstdio>
#include <vector>
#include<deque> 
#include<iostream>
using namespace std;

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        deque<int> buffer;
        vector<int> res;

        for(int i=0; i<nums.size();++i)
        {
            while(!buffer.empty() && nums[i]>=nums[buffer.back()]) buffer.pop_back();
            buffer.push_back(i);

            if(i>=k-1) res.push_back(nums[buffer.front()]);
            if(buffer.front()<= i-k + 1) buffer.pop_front();
        }
        return res;
    }
};
int main(){
    Solution test;
    vector<int> aa;
    aa.push_back(19);
    aa.push_back(-5);
    aa.push_back(2);
    aa.push_back(7);
    aa.push_back(6);
    aa.push_back(7);
    aa.push_back(5);
    aa.push_back(9);
    test.maxSlidingWindow(aa,3);
    return 0;
}