LeetCode: 239. Sliding Window Maximum

题目描述

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

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?

解题思路

利用滑动窗口计算。

AC 代码

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