二叉索引树——树状数组

int lowbit(int x){    return x&(-x);}int sum(int x){    int ret=0;    while(x>0)    {        ret+=c[x];        x-=lowbit(x);    }    return ret;}void add(int x,int d){    while(x<n)    {        c[x]+=d;        x+=lowbit(x);    }}