HDU 4262 Juggler

http://acm.hdu.edu.cn/showproblem.php?pid=4262

树状数组更新点的位置，并可以求出两点之间的有多少球

#include <stdio.h>
#define maxn  100001
int ans[maxn], n, b[maxn];

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

void mod(int x, int data)
{
    int i;
    for(i = x; i <= n; i+=lowbit(i))
    ans[i] += data;
}

int getSum(int x)
{
    int i, sum=0;
    for(i = x; i > 0; i -= lowbit(i))
       sum += ans[i];
    return  sum;   
}

int abs(int a)
{
    if(a < 0)  return -a;
    return a;
}

int main()
{
    long long  m, i, j, k, l, mark, sum, temp;
    while(~scanf("%lld",&n), n)
    {
        for(i = 1; i <= n; i++)
        {
            scanf("%lld",&m);
            b[m] = i;
            ans[i] = lowbit(i);
        }
        mark = 1;
        sum = 0;
        for(i = 1; i <= n; i++)
        {
            if(mark != b[i])
            {
                temp = abs(getSum(mark - 1)-getSum(b[i] - 1));
                sum += (temp > (n - i + 1 - temp ) ? (n - i + 1 - temp) : temp);
            }
            mark = b[i];
            mod(b[i], -1);
        }
        sum += n;
        printf("%I64d\n",sum);
    }
    return 0;
}