【LeetCode 0239】【大堆/双端队列】滑动窗口中的最大值

239. Sliding Window Maximum

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:

**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:

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

Constraints:

• 1 <= nums.length <= 10^5
• -10^4 <= nums[i] <= 10^4
• 1 <= k <= nums.length

Idea

* 使用最大堆
* 使用双端队列(*)

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number[]}
 */
var maxSlidingWindow = function(nums, k) {
    let window = [] // 存放数组元素在窗口内的索引
    let result = []
    for( let i=0; i < nums.length; i++){
        // 向右移动窗口
        if( i>=k && window[0] <= i-k ){
            window.shift();
        }
        // 将队尾窗口比当前值小的索引删除掉
        while( window.length > 0  && nums[window[window.length-1]] < nums[i] ){
            window.pop();
        }
        // 将当前所以加入
        window.push(i)
        // 收集当前窗口最大值
        if(i >= k-1 ){
            result.push(nums[window[0]]);
        }
    }
    return result
};