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239. Sliding Window Maximum

时间:2016-04-25 13:02:19      阅读:269      评论:0      收藏:0      [点我收藏+]

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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.

For example,
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].

Note: 
You may assume k is always valid, ie: 1 ≤ k ≤ input array‘s size for non-empty array.

Follow up:
Could you solve it in linear time?

 

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 1 Solution 1. Priority Queue
 2 public class Solution {
 3     class Pair implements Comparable<Pair>{
 4         public int key;
 5         public int idx;
 6         
 7         public Pair(int k, int id) {
 8             this.key = k;
 9             this.idx = id;
10         }
11         
12         @Override
13         public int compareTo(Pair p) {
14             return this.key < p.key ? 1 : (this.key == p.key ? 0 : -1); // reverse order, from Large to Small
15         }
16     }
17     
18     public int[] maxSlidingWindow(int[] nums, int k) {
19         if (nums.length == 0 || k <= 0) return new int[0];
20         
21         PriorityQueue<Pair> que = new PriorityQueue<Pair>();
22         int[] ret = new int[nums.length - k + 1];
23         int i = 0;
24         
25         for (i = 0; i < nums.length; i++) {
26             que.add(new Pair(nums[i], i));
27             while (que.peek().idx < i - k + 1) {
28                 que.poll();
29             }
30             if (i >= k-1) {
31                 ret[i-k+1] = que.peek().key;
32             }
33         }
34         
35         return ret;
36     }
37 }

 

239. Sliding Window Maximum

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原文地址:http://www.cnblogs.com/joycelee/p/5430378.html

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