Submission #35490545

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Source Code Expand

#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define op(x) ((x&1)?x+1:x-1)
#define odd(x) (x&1)
#define even(x) (!odd(x))
#define lc(x) (x<<1)
#define rc(x) (lc(x)|1)
#define lowbit(x) (x&-x)
#define mp(x,y) make_pair(x,y)
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
using namespace std;
const int MAXN=5010;
int n,m,a[MAXN];
set<int>S;
map<int,int>f;
void check(int u){
    int val=0,cnt=0;
    rep(i,1,n){
        int A=a[i]%u;
        if(cnt==0){
            val=A;cnt=1;
        }else{
            if(val==A)cnt++;
            else cnt--;
        }
    }
    if(cnt){
        cnt=0;
        rep(i,1,n)cnt+=(a[i]%u==val);
        if(cnt>(n/2)){
            cout<<u;exit(0);
        }
    }
}
int main(){
    cin>>n;
    rep(i,1,n)cin>>a[i];
    sort(a+1,a+1+n);
    if(odd(n)){
        int g=a[3]-a[1];
        rep(i,3,n)if(odd(i))g=__gcd(g,a[i]-a[i-2]);
        if(g>=3){
            cout<<g;
            return 0;
        }
    }
    rep(i,1,n-1){
        int d=a[i+1]-a[i];
        if(d%4==0)S.insert(4);
        rep(j,2,d){
            if(1ll*j*j>d)break;
            if(d%j==0){
                S.insert(j);
                while(d%j==0)d/=j;
            }
        }
        if(d!=1)S.insert(d);
    }
    for(auto u:S)if(u>=3)check(u);

    cout<<-1;

    return 0;
}

Submission Info

Judge Result