java实现树状数组

public class ArrayTree {
    private int[] arr;
    private int size;
    public ArrayTree(){
        this.arr=new int[10000];
        this.size=10000;
    }

    private int lowbit(int x){
        return x&(-x);
    }

    public void add(int pos,int k)
    {
        for(int i=pos;i<size;i+=lowbit(i)) arr[i]+=k;
    }

    public int sum(int pos){
        int res=0;
        for(int i=pos;i>=1;i-=lowbit(i)) res+=arr[i];
        return res;
    }

    public int sums(int l,int r)
    {
        return sum(r)-sum(l-1);
    }
}