Codeforces Round #626 Div2 D. Present（位掩码,二分）

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int maxn=4e5+5;
typedef long long LL;
int n,a[maxn],b[maxn],p[30],ans,MOD;

void init(){
    p[0]=1;
    for(int i=1;i<=26;++i)
        p[i]=p[i-1]<<1;
}

int bs1(int ll,int rr,int v){
    int l=ll,r=rr,mid;
    while(l<=r){
        mid=(l+r)>>1;
        if(b[mid]>=v) r=mid-1;
        else l=mid+1;
    }
    return l;
}

int bs2(int ll,int rr,int v){
    int l=ll,r=rr,mid;
    while(l<=r){
        mid=(l+r)>>1;
        if(b[mid]<=v) l=mid+1;
        else r=mid-1;
    }
    return r;
}

int main(){
    init();
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
        scanf("%d",&a[i]);
    for(int k=0;k<=24;++k){
        LL num=0;
        MOD=p[k+1];
        for(int i=1;i<=n;++i)
            b[i]=a[i]%MOD;
        sort(b+1,b+n+1);
        for(int i=1;i<n;++i){
            int le=max(p[k]-b[i],0),ri=p[k+1]-1-b[i];
            int l=bs1(i+1,n,le);
            int r=bs2(i+1,n,ri);
            num+=(LL)(r-l+1);
            if(b[i]<=p[k]) continue;
            le=p[k+1]+p[k]-b[i],ri=p[k+2]-2-b[i];
            l=bs1(i+1,n,le);
            r=bs2(i+1,n,ri);
            num+=(LL)(r-l+1);
        }
        if((int)(num%2)==1) ans+=p[k];
    }
    printf("%d\n",ans);
    return 0;
}