求助树状数组某两个代码块的区别qwq

int sum(int x){
	int ans=0;
	for(x;x>0;x-=lowbit(x))
		ans+=a[x];
	return ans;		
}
cout<<sum(y)-sum(x-1)<<endl;

for(y;y>0;y-=lowbit(y))
	ans+=a[y];
for(x-1;x>0;x-=lowbit(x))
	ans-=a[x];
cout<<ans<<endl;