[POJ] 2823 Sliding Window

Sliding Window
Time Limit: 12000MS     Memory Limit: 65536K
Total Submissions: 66136        Accepted: 18796
Case Time Limit: 5000MS
Description

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 position Minimum value   Maximum value
[1  3  -1] -3  5  3  6  7   -1  3
 1 [3  -1  -3] 5  3  6  7   -3  3
 1  3 [-1  -3  5] 3  6  7   -3  5
 1  3  -1 [-3  5  3] 6  7   -3  5
 1  3  -1  -3 [5  3  6] 7   3   6
 1  3  -1  -3  5 [3  6  7]  3   7
Your task is to determine the maximum and minimum values in the sliding window at each position. 

Input

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. 
Output

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. 
Sample Input

8 3
1 3 -1 -3 5 3 6 7
Sample Output

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

POJ Monthly--2006.04.28, Ikki

单调队列，感觉理解深刻了。

//Stay foolish,stay hungry,stay young,stay simple
#include<iostream>

using namespace std;

const int MAXN=1000005;

int q[MAXN],id[MAXN],head=1,tail;
int a[MAXN];
int n,k;

int main(){
    cin.sync_with_stdio(false);
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    for(int i=1;i<=n;i++){
        int v=a[i];
        while(tail>=head&&q[tail]>v) tail--;
        q[++tail]=v;
        id[tail]=i;
        while(id[head]<=i-k) head++;
        if(i>=k) cout<<q[head]<<" ";
    }
    cout<<endl;
    tail=0;head=1;
    for(int i=1;i<=n;i++){
        int v=a[i];
        while(tail>=head&&q[tail]<v) tail--;
        q[++tail]=v;
        id[tail]=i;
        while(id[head]<=i-k) head++;
        if(i>=k) cout<<q[head]<<" ";
    }
    return 0;
}