数据结构 树状数组

public class ffff { static int a[] = new int[9]; static int BIT[] = new int[9]; public static void main(String[] args) {  // TODO Auto-generated method stub  for (int i = 1; i <= 8; i++)   a[i] = i;  new ffff().build();  for (int i = 1; i <= 8; i++)   System.out.println(sum(i)); } static int sum(int end) {  int sum = 0;  while (end > 0) {   sum += BIT[end];   end -= lowbit(end);  }  return sum; } static int lowbit(int t) {  return t & (-t); } void build() {  for (int i = 1; i <= 8; i++) {   BIT[i] = a[i];   for (int j = i - 1; lowbit(i) > lowbit(j) && j != 0; j--)    BIT[i] += a[j];  } }}