[hdu3530]Subsequence （单调队列）

题意：求在一段序列中满足m<=max-min<=k的最大长度。

解题关键：单调队列+dp，维护前缀序列的最大最小值，一旦大于k，则移动左端点，取max即可。

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<iostream>
#include<cmath>
#define maxn 1000005
using namespace std;
typedef long long ll;
int n,m,k;
int qmin[maxn],qmax[maxn],a[maxn];
int main(){
    while(scanf("%d%d%d",&n,&m,&k)!=EOF){
        for(int i=1;i<=n;i++) scanf("%d",a+i);
        int head1=0,rear1=0,head2=0,rear2=0,now=1,ans=0;
        for(int i=1;i<=n;i++){
            while(head1<rear1&&a[qmin[rear1-1]]>a[i]) rear1--;
            while(head2<rear2&&a[qmax[rear2-1]]<a[i]) rear2--;
            qmin[rear1++]=i;
            qmax[rear2++]=i;
            while(head1<rear1&&head2<rear2&&a[qmax[head2]]-a[qmin[head1]]>k){
                if(qmin[head1]<qmax[head2]) now=qmin[head1++]+1;
                else now=qmax[head2++]+1;
            }
            if(head1<rear1&&head2<rear2&&a[qmax[head2]]-a[qmin[head1]]>=m){
                ans=max(ans,i-now+1);
            }
        }
        printf("%d\n",ans);
    }
}