主席树 - Luogu 1001 A+B problem

看着大佬们的解法我瑟瑟发抖
我用主席树写一写吧

#include<iostream>
#include<iomanip>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
inline int gotcha()
{
    register int _a=0;bool _b=1;register char _c=getchar();
    while((_c<'0' || _c>'9') && _c!='-')_c=getchar();
    if(_c=='-')_b=0,_c=getchar();
    while(_c>='0' && _c<='9')_a=_a*10+_c-48,_c=getchar();
    return _b?_a:-_a;
}
const int _ = 1000002,__ = 20*_;
int a[_],n,root[__]={0},ch[__][2]={0},da[__],cnt;
inline void plant(int &d,int l,int r)
{
    d=++cnt;
    if(l==r){da[d]=a[l];return;}
    int mid=(l+r)>>1;
    plant(ch[d][0],l,mid),plant(ch[d][1],mid+1,r);
}
inline void insert(int &d,int pre,int l,int r,int tar,int dat)
{
    d=++cnt,ch[d][0]=ch[pre][0],ch[d][1]=ch[pre][1],da[d]=da[pre];
    if(l==r){da[d]=dat;return;}
    int mid=(l+r)>>1;
    if(tar<=mid)insert(ch[d][0],ch[pre][0],l,mid,tar,dat);
    else insert(ch[d][1],ch[pre][1],mid+1,r,tar,dat);
}
inline int finder(int d,int l,int r,int tar)
{
    if(l==r)return da[d];
    int mid=(l+r)>>1;
    if(tar<=mid)return finder(ch[d][0],l,mid,tar);
    else return finder(ch[d][1],mid+1,r,tar);
}
int main()
{
    register int i;
    n=2;
    for(i=1;i<=n;i++)a[i]=gotcha();
    plant(root[0],1,n);
    i=finder(root[0],1,n,1)+finder(root[0],1,n,2);
    printf("%d\n",i);
    return 0;
}

常数巨大，不要被我误导……