树状数组的区间修改区间查询
设差分数组(c_i=a_i-a_{i-1})，
[ecause a_i= sum_{1}^{i}c_i
]
[ hereforesum_{i=1}^x a_i=sum_{i=1}^xsum_{j=1}^ic_j =sum_{i=1}^x (x-i+1)*c_i
]
[sum_{i=1}^x a_i=(x+1)sum_{i=1}^x c_i-sum_{i=1}^x c_i imes i
]
修改
void add(long long k,long long z)
{
for(long long i=k;i<=n;i+=(i& -i)) c[i]+=z,c1[i]+=(k-1)*z;
}
前缀和查询
long long qsum(long long k)
{
long long ans=0;
for(long long i=k;i>0;i-=(i & -i)) ans+=(long long)c[i]*k-c1[i];
return ans;
}
调用
add(x,y); add(x+1,-y);