Submission #675959

#	Time	Username	Problem	Language	Result	Execution time	Memory
675959		MrBrionix	Palindromic Partitions (CEOI17_palindromic)	C++17	100 / 100	5397 ms	107068 KiB

palindromic

#include<bits/stdc++.h>
using namespace std;
 
constexpr int MAXN = 1 << 20, LOGN = 21;
int table[LOGN][MAXN];
void build(int N, vector<int> &V) {
    copy(V.begin(), V.begin()+N, table[0]);
    for (int j = 1; j < LOGN; j++) {
        for (int i = 0; i + (1 << j) <= N; i++) {
            table[j][i]=min(table[j-1][i],
                table[j-1][i+(1<<j)/2]);
        }
    }
}
int query(int l, int r) {
    int k = 31 - __builtin_clz(r - l); // [l, r)
    return min(table[k][l], table[k][r-(1 << k)]);
}
 
template<class T> using V = vector<T>; 
using vi = V<int>;
#define sz(x) int((x).size())
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define each(a,x) for (auto& a: x)
#define all(x) begin(x), end(x)
 
struct SuffixArray {
  string S; int N; vi sa, isa, lcp; //N=sz(S)+1=n+1
  void init(string _S) { //$\mathcal{O}(n\log n)$
    N = sz(S = _S)+1; genSa(); genLcp();
  } //tested with $n \leq 5\cdot 10^5$ (226 ms)
  void genSa() { // sa has size sz(S)+1, sa[0]=sz(S)
    sa = isa = vi(N); sa[0] = N-1; iota(1+all(sa),0);
    sort(1+all(sa),[&](int a,int b){return S[a]<S[b];});
    FOR(i,1,N) { int a = sa[i-1], b = sa[i];
      isa[b] = i > 1 && S[a] == S[b] ? isa[a] : i; }
    for (int len = 1; len < N; len *= 2) { // currently
      // sorted by first len chars
      vi s(sa), is(isa), pos(N); iota(all(pos),0);
      each(t,s){
        int T=t-len;if(T>=0)sa[pos[isa[T]]++]=T;
      }
      FOR(i,1,N) {
        int a = sa[i-1], b = sa[i];
        // verify that nothing goes out of bounds
        isa[b] = is[a]==is[b]&&
          is[a+len]==is[b+len]?isa[a]:i;
      }
    }//sa[i]= indice (0-based) d'inizio i-esimo...
  }  //... prefisso più piccolo
  // isa[i] = x t.c. sa[x]=i
  //lcp[i]=lcp tra sa[i] e sa[i+1] ($0\leq i \leq n-1$)
  void genLcp(){
    lcp=vi(N-1); int h=0; //lcp[0]=lcp(sz(S),sa[1])=0
    F0R(b,N-1) { int a = sa[isa[b]-1];
      while (a+h < sz(S) && S[a+h] == S[b+h]) ++h;
      lcp[isa[b]-1] = h; if (h) h--; }
    build(N-1,lcp); // serve rmq (del booklet)
    //ma va modificato con vector<int>& anzichè int*
    //e V.begin() anzichè V
    //if we cut off first chars of two strings with...
  } //...lcp h then remaining portions still have lcp h-1
  //lcp of suffixes starting at a,b
  int getLCP(int a, int b){
    if (a == b) return sz(S)-a; // a,b sono 0-based
    int l = isa[a], r = isa[b]; if (l > r) swap(l,r);
    return query(l,r); // serve rmq (del booklet)
  }
};
 
void solve(){
    string s;
    int n;
    cin>>s;
    n=s.size();
    SuffixArray tmp;
    tmp.init(s);
    assert(tmp.lcp[0]==0);
    
    int last=0,ans=0;
    for(int i=0;i<s.size()/2;i++){
        if(s[last]==s[s.size()-1-i] && tmp.getLCP(last,s.size()-1-last-(i-last))>=(i-last+1)){
            last=i+1;
            ans+=2;
        }
    }
    
    if(last!=s.size()/2 || s.size()%2==1)ans++;
    cout<<ans<<"\n";
}
 
int main(){
    
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int t;
    cin>>t;
    
    while(t--)solve();
    
    return 0;
}

Compilation message (stderr)

palindromic.cpp: In function 'void solve()':
palindromic.cpp:82:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   82 |     for(int i=0;i<s.size()/2;i++){
      |                 ~^~~~~~~~~~~
palindromic.cpp:89:12: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   89 |     if(last!=s.size()/2 || s.size()%2==1)ans++;
      |        ~~~~^~~~~~~~~~~~
palindromic.cpp:74:9: warning: variable 'n' set but not used [-Wunused-but-set-variable]
   74 |     int n;
      |         ^

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 40 / 40