AT2412 最大の和

传送门

思路：

　　线段树暴力枚举区间，查询最大区间和。

Code:

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string>
#include<cstdlib>
#include<stack>
#include<vector>
#include<queue>
#include<deque>
#include<map>
#include<set>
using namespace std;
#define lck_max(a,b) ((a)>(b)?(a):(b))
#define lck_min(a,b) ((a)<(b)?(a):(b))
typedef long long LL;
const int maxn=1e5+;
const int INF=1e9+;
LL n,k,ans=-INF,sum[maxn<<],a[maxn];
inline LL read()
{
    LL kr=,xs=;
    char ls;
    ls=getchar();
    while(!isdigit(ls))
    {
        if(!(ls^))
            kr=-;
        ls=getchar();
    }
    while(isdigit(ls))
    {
        xs=(xs<<)+(xs<<)+(ls^);
        ls=getchar();
    }
    return xs*kr;
}
inline void out(LL xs)
{
    if(!xs) {putchar(); return;}
    if(xs<) putchar('-'),xs=-xs;
    int kr[],ls=;
    while(xs) kr[++ls]=xs%,xs/=;
    while(ls) putchar(kr[ls]+),ls--;
}
void build_sum(LL k,LL l,LL r)
{
    if(l==r) {sum[k]=a[l];return;}
    LL mid=l+r>>;
    if(l<=mid) build_sum(k<<,l,mid);
    if(mid<r) build_sum(k<<|,mid+,r);
    sum[k]=sum[k<<]+sum[k<<|];
}
LL query_sum(LL k,LL l,LL r,LL x,LL y)
{
    if(l>=x&&r<=y) return sum[k];
    //if(l>y||r<x) return 0;
    LL mid=l+r>>,res=;
    if(x<=mid) res+=query_sum(k<<,l,mid,x,y);
    if(mid<y) res+=query_sum(k<<|,mid+,r,x,y);
    return res;
}
int main()
{
    n=read();k=read();
    for(LL i=;i<=n;i++) a[i]=read();
    build_sum(,,n);
    for(LL i=k+;i<=n;i++)
        ans=lck_max(ans,query_sum(,,n,i-k+,i));
    out(ans),putchar('\n');
return ;
}