Numerical Array Template

Numerical Array Template

Detailed explanation of the principle of tree array: https://zhuanlan.zhihu.com/p/25185969

class BIT {
    
    
    int n;
    int[] tree;
    public BIT(int n) {
    
    
        this.n = n;
        this.tree = new int[n + 1];
    }
// 更新tree[i]到tree[n]的值
    public void update(int i, int delta) {
    
    

        while(i <= n) {
    
    
            tree[i] += delta;
            i += lowbit(i);
        }
    }
// 查询tree[1]到tree[i]的区间和
    public int query(int i) {
    
    
        int res = 0;
        while(i > 0) {
    
    
            res += tree[i];
            i -= lowbit(i);
        }
        return res;
    }
// 获得最后一位1的位置，而i & (i - 1)是最后一位1置为0，其他位不变
    public int lowbit(int i) {
    
    
        return i & (- i);
    }
}