BZOJ 2501 Soda Machine

BIT+离散化。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 200050
using namespace std;
int n,t[maxn],sum[maxn],ans=0,x[maxn],y[maxn],ha[maxn],cnt=0;
int lowbit(int x) {return (x&(-x));}
void add(int x,int val)
{
    for (int i=x;i<=cnt;i+=lowbit(i))
        t[i]+=val;
}
int ask(int x)
{
    int ret=0;
    for (int i=x;i>=1;i-=lowbit(i))
        ret+=t[i];
    return ret;
}
int find(int x)
{
    return lower_bound(ha+1,ha+cnt+1,x)-ha;
}
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%d%d",&x[i],&y[i]);
        ha[++cnt]=x[i];ha[++cnt]=y[i];
    }
    sort(ha+1,ha+cnt+1);cnt=unique(ha+1,ha+cnt+1)-ha-1;
    for (int i=1;i<=n;i++)
    {
        int a=find(x[i]),b=find(y[i]);
        add(a,1);add(b+1,-1);
    }
    for (int i=1;i<=cnt;i++) sum[i]=ask(i);
    for (int i=1;i<=cnt;i++) ans=max(ans,sum[i]);
    printf("%d
",ans);
    return 0;
}