codevs 1360 xth砍树 线段树不能再水的题了

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=200003;
const double mo=3.14;
double sum[N<<2];
void pushup(int rt){sum[rt]=sum[rt<<1]+sum[rt<<1|1];}
void build(int l,int r,int rt)
{
    if (l==r) {scanf("%lf",&sum[rt]); sum[rt]=sum[rt]*mo; return;}
    int mid=(l+r)>>1;
    build(l,mid,rt<<1);
    build(mid+1,r,rt<<1|1);
    pushup(rt);
}
double quest(int L,int R,int l,int r,int rt)
{
    if (L<=l&&r<=R) return sum[rt];
    int mid=(l+r)>>1;double ans=0;
    if (L<=mid) ans+=quest(L,R,l,mid,rt<<1);
    if (R>mid) ans+=quest(L,R,mid+1,r,rt<<1|1);
    return ans;
}
void cut(int x,int l,int r,int rt)
{
    if (l==r) {sum[rt]=0.0;return;}
    int mid=(l+r)>>1;
    if (x<=mid) cut(x,l,mid,rt<<1);
    if (x>mid) cut(x,mid+1,r,rt<<1|1);
    pushup(rt);
}
int main()
{
    int n,i,m,x,y;
    scanf("%d\n",&n);
    build(1,n,1);
    scanf("%d\n",&m);
    for (i=1;i<=m;++i)
    {
        scanf("%d %d\n",&x,&y);
        printf("%.2lf\n",quest(x,y,1,n,1));
        cut((x+y)>>1,1,n,1);
    }
    return 0;
}