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## Discussion of Problem 1590. Bacon’s Cipher

accepted - prefix function
Posted by Mikhail 16 May 2018 21:54
//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("avx")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

#define re return
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define sqrt(x) sqrt(abs(x))
#define mp make_pair
#define pi (3.14159265358979323846264338327950288419716939937510)
#define fo(i, n) for(int i = 0; i < n; ++i)
#define ro(i, n) for(int i = n - 1; i >= 0; --i)
#define unique(v) v.resize(unique(all(v)) - v.begin())

template <class T> T abs (T x) { re x > 0 ? x : -x; }
template <class T> T sqr (T x) { re x * x; }
template <class T> T gcd (T a, T b) { re a ? gcd (b % a, a) : b; }
template <class T> int sgn (T x) { re x > 0 ? 1 : (x < 0 ? -1 : 0); }

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<string> vs;
typedef double D;
typedef long double ld;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef unsigned long long ull;
typedef tree <pair<int, char>, null_type, less<pair<int, char>>, rb_tree_tag, tree_order_statistics_node_update> _tree;

void prefix_function (string &s, vi &p) {
int n = s.size();
p.resize(n, 0);
for (int i = 1; i < n; ++i) {
int j = p[i - 1];
while (j > 0 && s[i] != s[j]) j = p[j - 1];
if (s[i] == s[j]) ++j;
p[i] = j;
}
}

int main() {
string str, s;
cin >> str;
int ans = 0;
vi p;
for (int i = 1; i <= str.size(); ++i) {
s = str.substr(0, i);
reverse(all(s));
prefix_function(s, p);
ans += (int)s.size() - (*max_element(all(p)));
}
cout << ans << endl;
re 0;
}