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z_algorithm.cpp
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z_algorithm.cpp
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//
// Z-algorithm
// res[i] := S[i:] と S[0: ] との最長共通部分列の長さ
//
// verified:
// AtCoder ARC 055 C - ABCAC
// https://atcoder.jp/contests/arc055/tasks/arc055_c
//
// AtCoder ARC 060 F - 最良表現
// https://atcoder.jp/contests/arc060/tasks/arc060_d
//
#include <bits/stdc++.h>
using namespace std;
vector<int> Zalgo(const string &S) {
int N = (int)S.size();
vector<int> res(N);
res[0] = N;
int i = 1, j = 0;
while (i < N) {
while (i+j < N && S[j] == S[i+j]) ++j;
res[i] = j;
if (j == 0) {++i; continue;}
int k = 1;
while (i+k < N && k+res[k] < j) res[i+k] = res[k], ++k;
i += k, j -= k;
}
return res;
}
//------------------------------//
// Examples
//------------------------------//
void ARC_055_C() {
string S, T;
cin >> S;
T = S;
reverse(T.begin(), T.end());
int N = (int)S.size();
const auto &zs = Zalgo(S);
const auto &zt = Zalgo(T);
long long res = 0;
for (int i = N/2+1; i < N; ++i) {
int slen = zs[i];
int tlen = zt[N-i];
if (slen + tlen < N-i) continue;
int left = max(1, N-i-tlen);
int right = min(N-i-1, slen);
res += right - left + 1;
}
cout << res << endl;
}
void ARC_060_F() {
// 約数
auto divisor = [](long long n) -> vector<long long> {
vector<long long> res;
for (long long i = 1LL; i*i <= n; ++i) {
if (n%i == 0LL) {
res.push_back(i);
long long temp = n/i;
if (i != temp) res.push_back(temp);
}
}
sort(res.begin(), res.end());
return res;
};
string str;
cin >> str;
int n = (int)str.size();
vector<long long> divs = divisor(n);
long long syuuki = n;
for (auto d : divs) {
bool ok = true;
for (int j = 0; j + d < n; ++j) {
if (str[j] != str[j+d]) ok = false;
}
if (ok) syuuki = min(syuuki, d);
}
if (syuuki == n) cout << 1 << endl << 1 << endl;
else if (syuuki == 1) cout << n << endl << 1 << endl;
else {
string str2 = str;
reverse(str2.begin(), str2.end());
auto lcp = Zalgo(str);
auto lcp2 = Zalgo(str2);
vector<int> cannot_cut(n*2, 0);
for (int d = 1; d < n; ++d) {
if (cannot_cut[d]) continue;
for (int dd = d*2; dd < n; dd += d) {
if (lcp[d] >= dd - d) cannot_cut[dd] = true;
if (lcp2[d] >= dd - d) cannot_cut[n-dd] = true;
}
}
int con = 0;
for (int i = 1; i < n; ++i) if (!cannot_cut[i]) ++con;
cout << 2 << endl << con << endl;
}
}
int main() {
ARC_055_C();
//ARC_060_F();
}