Sliding Window Maximum

原题: https://leetcode.com/problems/sliding-window-maximum/description/

题意: 给定一个数组,一个大小为k的滑动窗口从数组的最左端向最右端移动。你只可以看到窗口中的k个数字。每一次窗口向右边移动一步。

约定:(1)可以假设k总是有效的,也就是说:1 ≤ k ≤ 输入数组的大小,并且数组非空。

例子: 

Given nums = [1,3,-1,-3,5,3,6,7], and k = 3
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
Therefore, return the max sliding window as [3,3,5,5,6,7]

标签: sliding、window、窗口、maximum、左端、面试
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  • Bingo
    2017-08-18 17:45:35 1楼#1层
    Python:
    class Solution:
        # @param {integer[]} nums
        # @param {integer} k
        # @return {integer[]}
        def maxSlidingWindow(self, nums, k):
            dq = collections.deque()
            ans = []
            for i in range(len(nums)):
                while dq and nums[dq[-1]] <= nums[i]:
                    dq.pop()
                dq.append(i)
                if dq[0] == i - k:
                    dq.popleft()
                if i >= k - 1:
                    ans.append(nums[dq[0]])
            return ans
  • Bingo
    2017-08-18 17:46:16 2楼#1层
    C++:
    class Solution {
    public:
        vector<int> maxSlidingWindow(vector<int>& nums, int k) {
            vector<int> res;
            deque<int> q;
            for (int i = 0; i < nums.size(); ++i) {
                if (!q.empty() && q.front() == i - k) q.pop_front();
                while (!q.empty() && nums[q.back()] < nums[i]) q.pop_back();
                q.push_back(i);
                if (i >= k - 1) res.push_back(nums[q.front()]);
            }
            return res;
        }
    };
  • Bingo
    2017-08-18 17:47:11 3楼#1层
    Java:
     public static int[] slidingWindowMax(final int[] in, final int w) {
        final int[] max_left = new int[in.length];
        final int[] max_right = new int[in.length];
    
        max_left[0] = in[0];
        max_right[in.length - 1] = in[in.length - 1];
    
        for (int i = 1; i < in.length; i++) {
            max_left[i] = (i % w == 0) ? in[i] : Math.max(max_left[i - 1], in[i]);
    
            final int j = in.length - i - 1;
            max_right[j] = (j % w == 0) ? in[j] : Math.max(max_right[j + 1], in[j]);
        }
    
        final int[] sliding_max = new int[in.length - w + 1];
        for (int i = 0, j = 0; i + w <= in.length; i++) {
            sliding_max[j++] = Math.max(max_right[i], max_left[i + w - 1]);
        }
        return sliding_max;
    }
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