BZOJ 4411: [Usaco2016 Feb]Load balancing 线段树+二分

code:

#include <bits/stdc++.h>
#define N 100060
#define M 1000000
#define lson x<<1
#define rson x<<1|1
#define ll long long
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int n,num[N*10],ans=N,X0,X1;
struct node
{
    int x0,x1;
}t[N*10*4];
struct Point
{
    int x,y;
    friend bool operator<(Point a,Point b) { return a.y<b.y; }
}a[N];
void pushup(int x)
{
    t[x].x0=t[lson].x0+t[rson].x0;
    t[x].x1=t[lson].x1+t[rson].x1;
}
void build(int x,int l,int r)
{
    if(l==r)
    {
        t[x].x0=num[l];
        t[x].x1=0;
        return;
    }
    int mid=(l+r)>>1;
    build(lson,l,mid);
    build(rson,mid+1,r);
    pushup(x);
}
void update(int x,int l,int r,int p)
{
    if(l==r)
    {
        t[x].x0--,t[x].x1++;
        return;
    }
    int mid=(l+r)>>1;
    if(p<=mid)  update(lson,l,mid,p);
    else update(rson,mid+1,r,p);
    pushup(x);
}
int ask(int x,int l,int r,int x0,int x1)
{
    if(l==r) return l;
    int mid=(l+r)>>1;
    int sum0=x0+t[lson].x0,sum1=x1+t[lson].x1;
    if(max(sum0,sum1)>=max(t[1].x0-sum0,t[1].x1-sum1))
    {
        return ask(lson,l,mid,x0,x1);
    }
    else
    {
        return ask(rson,mid+1,r,sum0,sum1);
    }
}
void qsum(int x,int l,int r,int L,int R)
{
    if(L>R) return;
    if(l>=L&&r<=R)
    {
        X0+=t[x].x0;
        X1+=t[x].x1;
        return;
    }
    int mid=(l+r)>>1;
    if(L<=mid)  qsum(lson,l,mid,L,R);
    if(R>mid)   qsum(rson,mid+1,r,L,R);
}
int main()
{
    // setIO("input");
    int i,j;
    scanf("%d",&n);
    for(i=1;i<=n;++i) scanf("%d%d",&a[i].x,&a[i].y), num[a[i].x]++;
    sort(a+1,a+1+n);
    build(1,1,M);
    for(i=1,j;i<=n;i=j)
    {
        j=i;
        while(j<=n&&a[j].y==a[i].y)  update(1,1,M,a[j].x),++j;
        int pos=ask(1,1,M,0,0);
        X0=0,X1=0,qsum(1,1,M,1,pos);
        ans=min(ans,max(X0,X1));
        X0=0,X1=0,qsum(1,1,M,1,pos-1);
        ans=min(ans,max(t[1].x0-X0,t[1].x1-X1));
    }
    printf("%d\n",ans);
    return 0;
}