[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=;i<=n;i++) scanf("%d",a+i);
         int head1=,rear1=,head2=,rear2=,now=,ans=;
         for(int i=;i<=n;i++){
             while(head1<rear1&&a[qmin[rear1-]]>a[i]) rear1--;
             while(head2<rear2&&a[qmax[rear2-]]<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++]+;
                 else now=qmax[head2++]+;
             }
             if(head1<rear1&&head2<rear2&&a[qmax[head2]]-a[qmin[head1]]>=m){
                 ans=max(ans,i-now+);
             }
         }
         printf("%d\n",ans);
     }
 }