建树的时候对add和mul的初始化要放在if外面
大概这样：
```cpp
void build(int l,int r,int p)
{
add[p] = 0 , mul[p] = 1 ；
if(l==r)
{
sum[p] = a[l] % m ;
return ;
}
int mid = (l+r)/2;
build(l,mid,lc) , build(mid+1,r,rc) , pushup(p);
}
```
by Shirley_ninefish @ 2023-11-13 17:09:01
@[Shirley_ninefish](/user/796071) 谢谢,我脑抽了
by acheve_1k @ 2023-11-17 11:06:49