【HDU1514】Stars（树状数组）

绝对大坑。千万记住树状数组0好下标位置是虚拟节点。详见大白书P195。其实肉眼看也能得出，在add（有的也叫update）的点修改操作中如果传入0就会死循环。最后TLE。所以下标+1解决问题。上代码！

 #include <iostream>
 #include <cstring>
 #include <cstdlib>
 #include <cstdio>
 #include <algorithm>
 #include <numeric>
 #include <cctype>
 #include <cmath>
 using namespace std;

 const int V =  + ;
 const int M =  + ;
 int C[V], res[M];

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

 int sum (int x) {
     int ret = ;
     while (x > ) {
         ret += C[x]; x -= lowbit(x);
     }
     return ret;
 }

 void add (int x, int d) {
     while (x <= V) {
         C[x] += d; x += lowbit(x);
     }
 }

 int main () {
     int n, x, y;
     while (~scanf("%d", &n)) {
         memset(C, , sizeof(C));
         memset(res, , sizeof(res));

         for (int i =  ; i < n; ++ i) {
             scanf ("%d %d", &x, &y);
             res[sum(x + )] ++;
             add(x + , );
         }
         for (int i =  ; i < n; ++ i) {
             printf ("%d\n", res[i]);
         }
     }
     return ;
 }