[Data structure] C program implementation of tree array

int tree[ 100001 ]; // Tree array, used to take the sum of the data in the interval [x, y]

/*
 & Special operation, the value (decimal) of t&(-t) is the position where the first 1 appears from right to left in t in binary.
 Combined with the special properties of tree-like arrays, this value is useful
 */
int lowbit(int t)
{
    return t&(-t);
}
/*
 Suppose that the data at the array number x has been changed, so that the data at the x position has an increment v
 Modify the tree array as follows, so that the relevant sums containing x-bit data are increased by v
 According to the nature of the tree array, that is, add v to the data with subscripts x, x+lowbit(x), x+lowbit(x+lowbit(x))....
 */
void add(int x,int v)
{
    for(int i=x; i<=100000; i+=lowbit(i)) tree[i]+=v;
}
/*
 Take the sum of the data in the interval [0,x]
*/
int getsum(int x)
{
    int ans=0;
    for(int i=x;i>0;i-=lowbit(i))
        ans += tree[i];
    return years;
}
/*
 Binary search to further reduce the time complexity
 */
int binarySearch(int l, int r, int median)
{
    int mid ;
    while (l<=r)
    {
        mid = (l+r)/2;
        if (getsum(mid)<median)  l = mid+1;
        //注意此处是 >=
        else if (getsum(mid)>=median) r = mid-1;
        else return mid;
    }
    return l;
}