HDU 1541 Stars 树状数组

看完题解自己敲了一遍 还需要加深理解吧

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
int c[50000],num[50000];
int N=32100;
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<=N)
    {
        c[x]+=d;
        x+=lowbit(x);
    }
}
int main()
{
    int t;
    int i,j;
    while(cin>>t)
    {
        memset(c,0,sizeof(c));
        memset(num,0,sizeof(num));
        for(i=0;i<t;i++)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            num[sum(x+1)]++;
            add(x+1,1);
        }
        for(i=0;i<t;i++)
        {
            printf("%d\n",num[i]);
        }
    }
    return 0;
}