树状数组模板

 

#define lowbit(x) x&(-x)

int c[maxn];

int getsum(int x){
	int ret = 0;
	for( ; x > 0; ret += c[x], x -= lowbit(x));
	return ret;
}

void update(int x, int val){
	for ( ; x < maxn; c[x] += val, x += lowbit(x));
}