【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！

 

 1 #include <iostream>

 2 #include <cstring>

 3 #include <cstdlib>

 4 #include <cstdio>

 5 #include <algorithm>

 6 #include <numeric>

 7 #include <cctype>

 8 #include <cmath>

 9 using namespace std;

10 

11 const int V = 32000 + 10;

12 const int M = 15000 + 10;

13 int C[V], res[M];

14 

15 int lowbit (int x) {

16     return x & -x;

17 }

18 

19 int sum (int x) {

20     int ret = 0;

21     while (x > 0) {

22         ret += C[x]; x -= lowbit(x);

23     }

24     return ret;

25 }

26 

27 void add (int x, int d) {

28     while (x <= V) {

29         C[x] += d; x += lowbit(x);

30     }

31 }

32 

33 int main () {

34     int n, x, y;

35     while (~scanf("%d", &n)) {

36         memset(C, 0, sizeof(C));

37         memset(res, 0, sizeof(res));

38 

39         for (int i = 0 ; i < n; ++ i) {

40             scanf ("%d %d", &x, &y);

41             res[sum(x + 1)] ++;

42             add(x + 1, 1);

43         }

44         for (int i = 0 ; i < n; ++ i) {

45             printf ("%d\n", res[i]);

46         }

47     }

48     return 0;

49 }