Submission #18634

#	Time	Username	Problem	Language	Result	Execution time	Memory
18634		mindol	Three Friends (BOI14_friends)	C++14	100 / 100	144 ms	92524 KiB

friends

#include<iostream>
#include<memory.h>
#include<string>
using namespace std;

const int mod=1e9+7;
int len;
string s,a,b;

int dp[1000002][2];

int f(int st,bool use)
{
    if(~dp[st][use]) return dp[st][use];
    if(st==b.size())
    {
        if(!use) return dp[st][use]=1;
        else return dp[st][use]=(a[st]==b[st-1]);
    }
    int res=use?0:f(st+1,true);
    if(a[st]!=b[st-use]) return dp[st][use]=res;
    else return dp[st][use]=f(st+1,use)+res;
}

int main()
{
    cin>>len>>s;
    if(!(len&1) || len==1) { cout<<"NOT POSSIBLE"; return 0; }
    if(s.substr(0,len/2)==s.substr(len/2+1,len/2)) { cout<<s.substr(0,len/2); return 0; }

    a=s.substr(0,len/2+1);
    b=s.substr(len/2+1,len/2);
    memset(dp,-1,sizeof(dp));
    int cnt1=f(0,false);

    a=s.substr(len/2,len/2+1);
    b=s.substr(0,len/2);
    memset(dp,-1,sizeof(dp));
    int cnt2=f(0,false);

    if(cnt1+cnt2==0) cout<<"NOT POSSIBLE";
    else if(cnt1 && cnt2) cout<<"NOT UNIQUE";
    else cout<<(cnt1?s.substr(len/2+1,len/2):s.substr(0,len/2));

    return 0;
}

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