Submission #220146

#	Time	Username	Problem	Language	Result	Execution time	Memory
220146		LittleFlowers__	Palindromes (APIO14_palindrome)	C++14	23 / 100	1097 ms	41048 KiB

palindrome

#include <bits/stdc++.h>
using namespace std;
#define in ({int x=0;int c=getchar(),n=0;for(;!isdigit(c);c=getchar()) n=(c=='-');for(;isdigit(c);c=getchar()) x=x*10+c-'0';n?-x:x;})
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define fasty ios_base::sync_with_stdio(0),cin.tie(0);
#define forinc(a,b,c) for(int a=b,_c=c;a<=_c;++a)
#define fordec(a,b,c) for(int a=b,_c=c;a>=_c;--a)
#define forv(a,b) for(auto&a:b)
#define fi first
#define se second
#define pb push_back
#define ii pair<int,int>
#define mt make_tuple
#define all(a) a.begin(),a.end()
#define reset(f, x) memset(f, x, sizeof(f))
#define bit(x,i) ((x>>(i-1))&1)
#define on(x,i) (x|(1ll<<(i-1)))
#define off(x,i) (x&~(1<<(i-1)))
#define gg exit(0);

const int N=300010,
          M=1000000007;

int n,gap,ret;
int pos[N],sa[N],tmp[N],lcp[N],ln[N];
int f[22][N];
string s;

unsigned long long pw1[N], h1[N], g1[N];
long long pw2[N], h2[N], g2[N];

int cmp(int i,int j){
    if(pos[i]!=pos[j]) return pos[i]<pos[j];
    i+=gap, j+=gap;
    return i<=n && j<=n ? pos[i]<pos[j] : i>j;
}

int que(int i,int j){
    int t=ln[j-i+1];
    return min(f[t][i],f[t][j-(1<<t)+1]);
}

int palin(int i,int j){
    return h1[j]-h1[i-1]*pw1[j-i+1] == g1[i]-g1[j+1]*pw1[j-i+1] &&
           (h2[j]-h2[i-1]*pw2[j-i+1]%M+M)%M == (g2[i]-g2[j+1]*pw2[j-i+1]%M+M)%M;
}

main(){
    #define task "palindrome"
    //freopen(task".inp","r",stdin);
    //freopen(task".out","w",stdout);
    fasty;

    cin>>s; n=s.size(); s=" "+s;

    forinc(i,0,n) pw1[i]=i?pw1[i-1]*19937:1, pw2[i]=i?pw2[i-1]*47%M:1;
    forinc(i,1,n) sa[i]=i, pos[i]=s[i], ln[i]=log2(i);
    forinc(i,1,n) h1[i]=h1[i-1]*19937+s[i], h2[i]=(h2[i-1]*47+s[i])%M;
    fordec(i,n,1) g1[i]=g1[i+1]*19937+s[i], g2[i]=(g2[i+1]*47+s[i])%M;

    for(gap=1;;gap+=gap){
        sort(sa+1,sa+n+1,cmp);
        forinc(i,1,n-1) tmp[i+1]=tmp[i]+cmp(sa[i],sa[i+1]);
        forinc(i,1,n) pos[sa[i]]=tmp[i]+1;
        if(tmp[n]==n-1) break;
    }
    for(int i=1,k=0;i<=n;++i){
        for(int j=sa[pos[i]+1];s[i+k]==s[j+k];) k++;
        lcp[pos[i]]=k;
        if(k) k--;
    }

    forinc(i,1,n) f[0][i]=lcp[i];
    forinc(j,1,20) forinc(i,1,n){
        if(i+(1<<j)>n+1) continue;
        f[j][i]=min(f[j-1][i],f[j-1][i+(1<<j-1)]);
    }
    forinc(len,1,n){
        int le,mi,ri,lf,rt;
        //for(int l=1;l+len-1<=n;l+=len){
        forinc(l,1,n-len+1){
            int r=l+len-1;
            if(!palin(l,r)) continue;
            lf=rt=pos[l];
            le=pos[l],ri=n;
            while(le<=ri){
                mi=(le+ri)/2;
                if(que(pos[l],mi-1)>=len) rt=mi, le=mi+1;
                else ri=mi-1;
            }
            le=1,ri=pos[l];
            while(le<=ri){
                mi=(le+ri)/2;
                if(que(mi,pos[l]-1)>=len) lf=mi, ri=mi-1;
                else le=mi+1;
            }
            ret=max(ret,len*(rt-lf+1));
        }
    }
    cout<<ret;
}

Compilation message (stderr)

palindrome.cpp:49:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main(){
      ^
palindrome.cpp: In function 'int main()':
palindrome.cpp:77:45: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
         f[j][i]=min(f[j-1][i],f[j-1][i+(1<<j-1)]);
                                            ~^~

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27