Submission #520182

#	Time	Username	Problem	Language	Result	Execution time	Memory
520182		krit3379	세 명의 친구들 (BOI14_friends)	C++14	0 / 100	239 ms	66088 KiB

friends

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


long long bp1[N],hx1[N],p1=37,mod1=1e9+7,pre1,pre11,pre12,suf1,suf11,suf12,ans;
long long bp2[N],hx2[N],p2=31,mod2=3e9+7,pre2,pre21,pre22,suf2,suf21,suf22;
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;}
    bp1[0]=bp2[0]=1;
    for(i=1;i<=n;i++)bp1[i]=(bp1[i-1]*p1)%mod1;
    for(i=1;i<=n;i++)bp2[i]=(bp2[i-1]*p2)%mod2;
    for(i=1;i<=n;i++){
        hx1[i]=(hx1[i-1]*p1+s[i]-'A'+1)%mod1;
        hx2[i]=(hx2[i-1]*p2+s[i]-'A'+1)%mod2;
    }
    suf1=((hx1[n]-hx1[n/2+1]*bp1[n/2])%mod1+mod1)%mod1;
    suf2=((hx2[n]-hx2[n/2+1]*bp2[n/2])%mod2+mod2)%mod2;
    for(i=1;i<=n/2;i++){
        pre11=(hx1[i-1]*bp1[n/2-i+1])%mod1;
        pre12=(hx1[n/2+1]-hx1[i]*bp1[n/2+1-i])%mod1;
        pre1=((pre11+pre12)%mod1+mod1)%mod1;
        pre21=(hx2[i-1]*bp2[n/2-i+1])%mod2;
        pre22=(hx2[n/2+1]-hx2[i]*bp2[n/2+1-i])%mod2;
        pre2=((pre21+pre22)%mod2+mod2)%mod2;
        if(pre1==suf1&&pre2==suf2)ans++,en=true;
    }
    pre1=hx1[n/2];
    pre2=hx2[n/2];
    if(pre1==suf1&&pre2==suf2)ans++,mid=true;
    for(i=n/2+2;i<=n;i++){
        suf11=((hx1[i-1]-hx1[n/2]*bp1[i-1-n/2])*bp1[n-i])%mod1;
        suf12=(hx1[n]-hx1[i]*bp1[n-i])%mod1;
        suf1=((suf11+suf12)%mod1+mod1)%mod1;
        suf21=((hx2[i-1]-hx2[n/2]*bp2[i-1-n/2])*bp2[n-i])%mod2;
        suf22=(hx2[n]-hx2[i]*bp2[n-i])%mod2;
        suf2=((suf21+suf22)%mod2+mod2)%mod2;
        if(pre1==suf1&&pre2==suf2)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:13:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   13 |     scanf("%d %s",&n,s+1);
      |     ~~~~~^~~~~~~~~~~~~~~~

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