來點(diǎn)硬核抽象——線段樹的正確用法：

#include<bits/stdc++.h>

using namespace std;

namespace IO

{

bool isdigit(const char x)

{

return x>='0'&&x<='9';

}

struct reader

{

template<typename T> reader& operator >> (T &x)

{

x=0;

bool f=0;

char c=getchar();

while (!isdigit(c)) f=c=='-'?1:f,c=getchar();

while (isdigit(c)) x=(x<<1)+(x<<3)+(c^'0'),c=getchar();

x=f?-x:x;

return *this;

}

reader& operator >> (double &x)

{

x=0;

bool f=0;

int t=0;

char c=getchar();

while (!isdigit(c)&&c!='.') f=c=='-'?1:f,c=getchar();

while (isdigit(c)&&c!='.') x=x*10+(c^'0'),c=getchar();

if (c!='.')

{

x=f?-x:x;

return *this;

}

c=getchar();

double y=0;

while (isdigit(c)) y=y*10+(c^48),t++,c=getchar();

while (t--) y/=10.0;

x+=y;

x=f?-x:x;

return *this;

}

reader& operator >> (char &x)

{

x=getchar();

while (x=='\n'||x==' '||x=='\r') x=getchar();

return *this;

}

reader& operator >> (char *x)

{

int l=0;

char c=getchar();

while (c==' '||c=='\n'||c=='\r') c=getchar();

while (c!=' '&&c!='\n'&&c!='\r') x[++l]=c,c=getchar();

return *this;

}

void getline(char *x)

{

int l=0;

char c=getchar();

while (c=='\n'||c=='\r') c=getchar();

while (c!='\n'&&c!='\r') x[++l]=c,c=getchar();

}

reader& operator >> (string &x)

{

x="";

char c=getchar();

while (c==' '||c=='\n'||c=='\r') c=getchar();

while (c!=' '&&c!='\n'&&c!='\r') x=x+c,c=getchar();

return *this;

}

void getline(string &x)

{

x="";

char c=getchar();

while (c=='\n'||c=='\r') c=getchar();

while (c!='\n'&&c!='\r') x=x+c,c=getchar();

}

}cin;

const char endl='\n',tab='\t',null='\0';

struct writer

{

template<typename T>writer& operator << (T x)

{

if (x<0) putchar('-'),x=-x;

int s[40],t=0;

while (x) s[++t]=x%10,x/=10;

if (!t) putchar('0');

while (t) putchar(s[t--]+'0');

return *this;

}

writer& operator << (double x)

{

if (x<0) putchar('-'),x=-x;

int y=x;

x-=y*1.0;

int s[40],t=0;

while (y) s[++t]=y%10,y/=10;

if (!t) putchar('0');

while (t) putchar(s[t--]+'0');

putchar('.');

for (int i=0;i<6;i++) x*=10;

y=x;

while (y) s[++t]=y%10,y/=10;

for (int i=0;i<6-t;i++) putchar('0');

while (t) putchar(s[t--]+'0');

return *this;

}

writer& operator << (const char x)

{

putchar(x);

return *this;

}

writer& operator << (char *x)

{

int t=0;

while (x[t]) putchar(x[t++]);

return *this;

}

writer& operator << (const char *x)

{

int t=0;

while (x[t]) putchar(x[t++]);

return *this;

}

writer& operator << (string x)

{

int t=0,l=x.size();

while (t<l) putchar(x[t++]);

return *this;

}

}cout;

}

namespace main_code

{

const int N=1e5+10;

int a[N],sum[N<<2],ad[N<<2];

int tot=0;

void build(int k,int l,int r)

{

if (l==r)

{

sum[k]=a[++tot];

return;

}

int mid=l+r>>1;

build(k<<1,l,mid);

build(k<<1|1,mid+1,r);

sum[k]=sum[k<<1]+sum[k<<1|1];

}

void add(int k,int l,int r,int z)

{

ad[k]+=z;

sum[k]+=z*(r-l+1);

}

void pushdown(int k,int l,int r,int mid)

{

add(k<<1,l,mid,ad[k]);

add(k<<1|1,mid+1,r,ad[k]);

ad[k]=0;

}

void modify(int k,int l,int r,int x,int y,int z)

{

if (r<x||l>y) return;

if (l>=x&&r<=y)

{

add(k,l,r,z);

return;

}

int mid=l+r>>1;

if (ad[k]) pushdown(k,l,r,mid);

if (x<=mid) modify(k<<1,l,mid,x,y,z);

if (mid<y) modify(k<<1|1,mid+1,r,x,y,z);

sum[k]=sum[k<<1]+sum[k<<1|1];

}

int query(int k,int l,int r,int x,int y)

{

if (r<x||l>y) return 0;

if (l>=x&&r<=y) return sum[k];

int mid=l+r>>1;

if (ad[k]) pushdown(k,l,r,mid);

int ans=0;

if (x<=mid) ans+=query(k<<1,l,mid,x,y);

if (mid<y) ans+=query(k<<1|1,mid+1,r,x,y);

return ans;

}

void main()

{

IO::cin>>a[1]>>a[2];

build(1,1,2);

IO::cout<<query(1,1,2,1,2)<<IO::endl;

}

}

signed main()

{

main_code::main();

return 0;

}