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2013
11-12

POJ 2823 Sliding Window [解题报告] Java

Sliding Window

问题描述 :

An array of size n ≤ 106 is given to you. 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 rightwards by one position. Following is an example:

The array is [1 3 -1 -3 5 3 6 7], and k is 3.
Window positionMinimum valueMaximum value
[1  3  -1] -3  5  3  6  7 -13
 1 [3  -1  -3] 5  3  6  7 -33
 1  3 [-1  -3  5] 3  6  7 -35
 1  3  -1 [-3  5  3] 6  7 -35
 1  3  -1  -3 [5  3  6] 7 36
 1  3  -1  -3  5 [3  6  7]37

Your task is to determine the maximum and minimum values in the sliding window at each position.

输入:

The input consists of two lines. The first line contains two integers n and k which are the lengths of the array and the sliding window. There are n integers in the second line.

输出:

There are two lines in the output. The first line gives the minimum values in the window at each position, from left to right, respectively. The second line gives the maximum values.

样例输入:

8 3
1 3 -1 -3 5 3 6 7

样例输出:

-1 -3 -3 -3 3 3
3 3 5 5 6 7

解题代码:

import java.util.Scanner;   
public class Main{   
    Scanner scan=new Scanner(System.in);   
    int n,k;   
    int[] queue=new int[1000005];   
    int[] Index=new int[1000005];   
    int[] arr=new int[1000005];   
    int[] MIN=new int[1000005];   
    int[] MAX=new int[1000005];   
    public static void main(String[] args){   
        new Main().run();   
    }   
    void run(){   
        n=scan.nextInt();   
        k=scan.nextInt();   
        if(k>n)   
            k=n;   
        for(int i=1;i<=n;i++)   
        {   
            arr[i]=scan.nextInt();   
        }   
        GetMin();   
        GetMax();   
        for(int i=0;i<=(n-k);i++)   
        {   
            System.out.print(MIN[i]+" ");   
        }   
        System.out.println();   
        for(int i=0;i<=(n-k);i++)   
        {   
            System.out.print(MAX[i]+" ");   
        }   
    }   
       
    void GetMin(){   
        int head=1;   
        int tail=0;   
        for(int i=1;i< k;i++)   
        {   
            while(head<=tail&&queue[tail]>arr[i])    
                tail--;   
            tail++;   
            queue[tail]=arr[i];   
            Index[tail]=i;   
        }   
        for(int i=k;i<=n;i++)   
        {   
            while(head<=tail&&queue[tail]>arr[i])   
                tail--;   
            tail++;   
            queue[tail]=arr[i];   
            Index[tail]=i;   
            while(Index[head]<=i-k)   
                head++;   
            MIN[i-k]=queue[head];   
        }   
    }   
       
    void GetMax(){   
        int head=1;   
        int tail=0;   
        for(int i=1;i< k;i++)   
        {   
            while(head<=tail&&queue[tail]< arr[i])    
                tail--;   
            tail++;   
            queue[tail]=arr[i];   
            Index[tail]=i;   
        }   
        for(int i=k;i<=n;i++)   
        {   
            while(head<=tail&&queue[tail]< arr[i])   
                tail--;   
            tail++;   
            queue[tail]=arr[i];   
            Index[tail]=i;   
            while(Index[head]<=i-k)   
                head++;   
            MAX[i-k]=queue[head];   
        }   
    }   
}