【2017多校】HDU6058 Kanade's sum 【链表】

题目链接

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枚举1到n,当i是第k大时，区间左端点到右端点 比i大的数必须=k-1个
将a[1..n]放链表里，枚举完i,则将i删去，则链表中所有元素都>当前枚举的数,O(k)即可统计出区间个数

#include<stdio.h>#include<bits/stdc++.h>#define ll long long#define pii pair<int,int>#define pll pair<ll,ll>#define MEM(a,x) memset(a,x,sizeof(a))#define lowbit(x) ((x)&-(x))using namespace std;const int N = 5e5+5;int a[N];int idx[N];list<int>::iterator Ref[N];list<int>ls;ll slove(int n,int k){    list<int>::iterator itL,itR;    int cntL,cntR;    ll ans=0;    for(int i=1;i<=n;++i){        itL=itR=Ref[i];        cntL=0,cntR=0;//itL-Ref[i]间多少个数比i大 ,itR-Ref[i]间...        for(int x=0;x<=k-1;++x){            while(cntR<k-1-x&&itR!=Ref[n+1]){                ++itR;                ++cntR;            }            if(cntR>k-1-x||itR==Ref[n+1]){                --itR;                --cntR;            }            if(cntR+cntL==k-1){                int CountL,CountR=CountL=1;                auto tmp=itL;                --tmp;                CountL=idx[*itL]-idx[*tmp];                tmp=itR;                ++tmp;                CountR=idx[*tmp]-idx[*itR];                ans+=(ll)CountL*CountR*i;            }            --itL;            if(itL==Ref[0]){                break;            }            ++cntL;        }        ls.erase(Ref[i]);    }    return ans;}int main(){    //freopen("/home/lu/code/r.txt","r",stdin);    //freopen("/home/lu/code/w.txt","w",stdout);    int T;    scanf("%d",&T);    while(T--){        int n,k;        scanf("%d%d",&n,&k);        ls.clear();        ls.push_back(0);        idx[0]=0;        Ref[0]=ls.begin();        for(int i=1;i<=n;++i){            scanf("%d",&a[i]);            ls.push_back(a[i]);            Ref[a[i]]=--ls.end();            idx[a[i]]=i;        }        ls.push_back(n+1);        idx[n+1]=n+1;        Ref[n+1]=--ls.end();        printf("%lld\n",slove(n,k));    }    return 0;}