Submission #180312

#	Time	Username	Problem	Language	Result	Execution time	Memory
180312		rzbt	Three Friends (BOI14_friends)	C++14	100 / 100	121 ms	50168 KiB

friends

#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define MAXN 2000006
typedef long long ll;


using namespace std;

const ll MOD = 1e9+9;

ll n;
char s[MAXN];
ll hes[MAXN];
ll stepen[MAXN];
ll res=0;
ll posl;
vector<ll> svi;
int main()
{

    scanf("%lld", &n);
    if(!(n&1)){
        printf("NOT POSSIBLE");
        return 0;
    }
    scanf("%s",s);
    hes[0]=s[0]-'A'+1;
    stepen[0]=1;
    for(ll i=1;i<n;i++){
        stepen[i]=(79*stepen[i-1])%MOD;
        hes[i]=(stepen[i]*(s[i]-'A'+1)+hes[i-1])%MOD;

    }
    for(ll i=0;i<n;i++){
        if(i<(n>>1)){
            ll th=hes[n>>1]-hes[i];
            if(i!=0)th+=hes[i-1]*stepen[1];
            th=(MOD+MOD+MOD+th)%MOD;
            th*=stepen[n/2];
            th%=MOD;
            if(th==(MOD+hes[n-1]-hes[n>>1])%MOD){
                res++,posl=i;
                svi.pb(th);
            }


        }
        if(i>(n>>1)){
            ll th=hes[n-1]-hes[i];
            th+=(hes[i-1]-hes[(n>>1)-1])*stepen[1];
            th=(MOD+MOD+MOD+th)%MOD;
            //printf("   %lld %lld\n",th,(hes[(n>>1)-1]*stepen[(n>>1)+1])%MOD );
            if(th==(hes[(n>>1)-1]*stepen[(n>>1)+1])%MOD  ){
                res++,posl=i;
                svi.pb(th);
            }
        }
        if(i==(n>>1)){
            ll ta=hes[(n>>1)-1];
            ll tb=(MOD+hes[n-1]-hes[(n>>1)])%MOD;
            //printf("%lld %lld    %lld %lld",ta,tb,stepen[(n>>1)+1],(ta*stepen[(n>>1)+1])%MOD);
            if(tb==(ta*stepen[(n>>1)+1])%MOD){
                res++,posl=i;
                svi.pb(tb);
            }

        }

    }
    if(res==0)printf("NOT POSSIBLE");
    else{
        for(int i=0;i<svi.size()-1;i++){
            if(svi[i]!=svi[i+1]){
                printf("NOT UNIQUE");
                return 0;
            }
        }
        ll gran=(n>>1);
        for(ll i=0;i<gran;i++){
            if(i==posl)gran++;
            else putchar(s[i]);
        }
    }

    return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int main()':
friends.cpp:76:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<svi.size()-1;i++){
                     ~^~~~~~~~~~~~~
friends.cpp:25:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%lld", &n);
     ~~~~~^~~~~~~~~~~~
friends.cpp:30:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%s",s);
     ~~~~~^~~~~~~~

• Subtask 1: 35 / 35
• Subtask 2: 65 / 65