K小数 树状数组

http://acm.xmu.edu.cn/JudgeOnline/problem.php?id=1165

树状数组+二分写的

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;
const int MAXN = 100000+10;


int c[MAXN];
bool a[MAXN];
bool flag;
int lowbit(int x)
{
    return x &(-x);
}

void update(int x,int v)
{
    while(x<MAXN)
    {
        c[x]+=v;
        x+=lowbit(x);
    }
}
int getSum(int x)
{
    int sum = 0;
    while(x>0)
    {
        sum+=c[x];
        x-=lowbit(x);
    }
    return sum;
}
int cal(int k,int l,int r)
{
    if(k>getSum(r))
    {
        return -1;
    }
    while(l<r)
    {
        int mid = (l+r)>>1;
        int t = getSum(mid);
        int tt = getSum(mid-1);
        if(t>=k&&tt<k)
          return mid;
        if(t>=k)
        {
            r = mid-1;
        }
        else
        {
            l = mid+1;
        }
    }
    return r;
}
int main()
{
    memset(c,0,sizeof(c));
    memset(a,false,sizeof(a));
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        int cmd,x;
        scanf("%d%d",&cmd,&x);
        if(cmd==1)
        {
            if(!a[x])
            {
              update(x,1);
              a[x] = true;
            }
        }
        else if(cmd==2)
        {
            if(a[x])
            {
               update(x,-1);
               a[x] = false;
            }
        }
        else
        {
            int ans = cal(x,1,MAXN-1);
            printf("%d\n",ans);
        }
    }
    return 0;
}