Submission #520177

#	Time	Username	Problem	Language	Result	Execution time	Memory
520177		krit3379	Three Friends (BOI14_friends)	C++14	0 / 100	147 ms	36500 KiB

friends

#include<bits/stdc++.h>
using namespace std;
#define N 2000005


long long bp[N],hx[N],p=31,mod=1e9+7,pre,pre1,pre2,suf,suf1,suf2,ans,pos;
char s[N];
bool st,mid,en;

int main(){
    int n,i;
    scanf("%d %s",&n,s+1);
    if(n%2==0){printf("NOT POSSIBLE");return 0;}
    bp[0]=1;
    for(i=1;i<=n;i++)bp[i]=(bp[i-1]*p)%mod;
    for(i=1;i<=n;i++){
        hx[i]=(hx[i-1]*p+s[i]-'A'+1)%mod;
    }
    suf=((hx[n]-hx[n/2+1]*bp[n/2])%mod+mod)%mod;
    for(i=1;i<=n/2;i++){
        pre1=(hx[i-1]*bp[n/2-i+1])%mod;
        pre2=(hx[n/2+1]-hx[i]*bp[n/2+1-i])%mod;
        pre=((pre1+pre2)%mod+mod)%mod;
        if(pre==suf)ans++,en=true;
    }
    pre=hx[n/2];
    if(pre==suf)ans++,mid=true;
    for(i=n/2+2;i<=n;i++){
        suf1=((hx[i-1]-hx[n/2]*bp[i-1-n/2])*bp[n/2-i+1])%mod;
        suf2=(hx[n]-hx[i]*bp[n-i])%mod;
        suf=((suf1+suf2)%mod+mod)%mod;
        if(pre==suf)ans++,st=true;
    }
    if(ans>1)printf("NOT UNIQUE");
    else if(ans){
        if(st||mid)for(i=1;i<=n/2;i++)printf("%c",s[i]);
        else for(i=n/2+2;i<=n;i++)printf("%c",s[i]);
    }
    else printf("NOT POSSIBLE");
    return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int main()':
friends.cpp:12:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   12 |     scanf("%d %s",&n,s+1);
      |     ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 35
• Subtask 2: 0 / 65