0239.滑动窗口最大值

https://leetcode.cn/problems/sliding-window-maximum/

方法一：滑动窗口+双端队列

时间复杂度 $O(n)$，空间复杂度 $O(k)$。

impl Solution {
    pub fn max_sliding_window(nums: Vec<i32>, k: i32) -> Vec<i32> {
        let mut ans = Vec::new();
        let mut deque = std::collections::VecDeque::new();
        for i in 0..nums.len() {
            while !deque.is_empty() && nums[*deque.back().unwrap()] < nums[i] {
                deque.pop_back();
            }
            deque.push_back(i);
            if i >= (k - 1) as usize {
                let elem = nums[*deque.front().unwrap()];
                ans.push(elem);
                if elem == nums[i + 1 - k as usize] {
                    deque.pop_front();
                }
            }
        }
        ans
    }
}