poj 2823 Sliding Window 单调队列

经典题

单调队列

Codes:

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>

using namespace std;
const int N = 1000000 + 5;

int cnt1,cnt2,n,k,a[N],cn;
int q1[N],q2[N],minn[N],maxx[N];
int ans1[N],ans2[N];
int main(){
    scanf("%d%d",&n,&k);
    int head1,tail1,head2,tail2;
    head1 = tail1 = head2 = tail2 = 0;
    for(int i = 1;i <= n;++ i){
        scanf("%d",&a[i]);
        while(head1 <= tail1 && a[i] < a[q1[tail1]]) {
            tail1 --;
        }
            
        q1[++ tail1] = i;
        
        while(q1[head1] < i - k + 1)    
            head1 ++;
        if(i >= k) 
            minn[++ cn] = q1[head1];
        while(head2 <= tail2 && a[i] > a[q2[tail2]]) 
            tail2 --;
        q2[++ tail2] = i;
        while(q2[head2] < i - k + 1) 
            head2 ++;
        if(i >= k)
            maxx[cn] = q2[head2];
    }
    for(int i = 1;i <= cn;++ i) 
        if(i == n) 
            cout << a[minn[i]]; 
        else 
            cout << a[minn[i]] << " ";
    cout << '
';
    for(int i = 1;i <= cn;++ i) 
        if(i == n) 
            cout << a[maxx[i]]; 
        else 
            cout << a[maxx[i]] << " ";
    return 0;
}