Tree array principle

Features:

①Quickly find the prefix sum $O\left(logn\right)$

②Modify a certain number $O\left(logn\right)$

operating:

①: Achievement

void add(int x, int c) {
    
     //树状数组的插入操作
	for (int i = x;i <= n;i += lowbit(i))tr[i] += c;
}

②: Interval query: 1 ~ x prefix sum

for(int i = x;i <= n;i += lowbit(i))res += c;

③: Single point modification:

for(int i = x;i;i -= lowbit(i))tr[i] += c;