【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 = 32000 + 10;
const int M = 15000 + 10;
int C[V], res[M];

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

int sum (int x) {
    int ret = 0;
    while (x > 0) {
        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, 0, sizeof(C));
        memset(res, 0, sizeof(res));

        for (int i = 0 ; i < n; ++ i) {
            scanf ("%d %d", &x, &y);
            res[sum(x + 1)] ++;
            add(x + 1, 1);
        }
        for (int i = 0 ; i < n; ++ i) {
            printf ("%d
", res[i]);
        }
    }
    return 0;
}