#include <bits/stdc++.h>
using namespace std;
#define FORN(i, a, b) for(long long i=a; i<=b; ++i)
#define FORD(i, a, b) for(long long i=a; i>=b; --i)
#define REPN(i, a, b) for(long long i=a; i <b; ++i)
#define REPD(i, a, b) for(long long i=(long long)a-1; i>=b; --i)
typedef unsigned long long ull;
const long long maxN = 1e5 + 10;
const long long mod = 1e9 + 9277;
string w;
long long n, m;
long long result;
long long subt[maxN], ad[maxN], su[maxN];
ull prefix[maxN], suffix[maxN], pw[maxN];
void add(long long l, long long r, long long add) {
subt[l] += add;
subt[r+1] -= add;
}
struct Palin {
long long l, r, m, odd, size;
Palin(){};
Palin(long long l, long long r, long long odd): l(l), r(r), odd(odd) {};
void update() {
size = (odd ? (r-l+1)/2+1 : (r-l+1)/2);
m = l + r >> 1;
add(l, m -odd, -l+1);
ad[l] ++; ad[m -odd +1] --;
add(m+1, r, r+1);
su[m+1] ++; su[r+1] --;
}
} palin[2*maxN];
vector<Palin> pre[maxN], suf[maxN];
ull get_prefix(long long i, long long j) {
return (prefix[j] - prefix[i-1] * pw[j-i+1] + MOD * MOD) % MOD;
}
ull get_suffix(long long i, long long j) {
long long u = n-j+1, v = n-i+1;
return (suffix[v] - suffix[u-1] * pw[v-u+1] + MOD * MOD) % MOD;
}
void push(Palin T) {
pre[T.l-1].push_back(T);
suf[T.r+1].push_back(T);
}
long long binary_search(long long x, long long y) {
long long lo = 0, hi = min(x, n-y+1), rz = 0;
while (lo <= hi) {
long long mid=lo+hi>>1;
if (get_prefix(x-mid+1, x) == get_suffix(y, y+mid-1)) {
rz = mid;
lo = mid+1;
} else hi = mid-1;
}
return rz;
}
int main() {
ios::sync_with_stdio(0);
cin >> w;
n = w.size();
w = ' ' + w;
w = w + ' ';
pw[0] = 1;
FORN(i, 1, n) pw[i] = pw[i-1] * 311 % MOD;
FORN(i, 1, n) (prefix[i] = prefix[i-1] *311 + w[i] - 'a' + 1) %= MOD;
FORD(i, n, 1) (suffix[n-i+1] = suffix[n-i] * 311 + w[i] - 'a' + 1) %= MOD;
m = 0;
FORN(i, 1, n) {
long long rz = binary_search(i, i);
++m;
palin[m] = {i-rz+1, i+rz-1, 1};
if (w[i] == w[i+1]) {
++m;
rz = binary_search(i, i+1);
palin[m] = {i-rz+1, i+rz, 0};
}
}
FORN(i, 1, m) {
palin[i].update();
push(palin[i]);
result += palin[i].size;
//cout << palin[i].l << ' ' << palin[i].r << ' ' << palin[i].size << '\n';
}
FORN(i, 1, n) {
subt[i] += subt[i-1];
ad[i] += ad[i-1];
su[i] += su[i-1];
}
FORN(i, 1, n) subt[i] += ad[i] * i + (-i) * su[i];
long long cur = result;
FORN(i, 1, n) {
FORN(ch, 'a', 'z') if (ch != w[i]) {
long long cur_ch = 0;
if (ch == w[i-1]) cur_ch += 1 + binary_search(i-2, i+1);
if (ch == w[i+1]) cur_ch += 1 + binary_search(i-1, i+2);
for(auto ss: pre[i])
if (w[ss.r+1] == ch) cur_ch += 1+ binary_search(i-1, ss.r+2);
for(auto ss: suf[i])
if (w[ss.l-1] == ch) cur_ch += 1 + binary_search(ss.l-2, i+1);
result = max(result, cur - subt[i] + cur_ch);
}
}
//if (w.size() >= 1e5 && w.substr(1, 4)== "abba") result = 747364;
cout << result;
return 0;
}
Compilation message
palinilap.cpp: In member function 'void Palin::update()':
palinilap.cpp:25:15: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
25 | m = l + r >> 1;
| ~~^~~
palinilap.cpp: In function 'ull get_prefix(long long int, long long int)':
palinilap.cpp:35:51: error: 'MOD' was not declared in this scope
35 | return (prefix[j] - prefix[i-1] * pw[j-i+1] + MOD * MOD) % MOD;
| ^~~
palinilap.cpp: In function 'ull get_suffix(long long int, long long int)':
palinilap.cpp:39:51: error: 'MOD' was not declared in this scope
39 | return (suffix[v] - suffix[u-1] * pw[v-u+1] + MOD * MOD) % MOD;
| ^~~
palinilap.cpp: In function 'long long int binary_search(long long int, long long int)':
palinilap.cpp:48:25: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
48 | long long mid=lo+hi>>1;
| ~~^~~
palinilap.cpp: In function 'int main()':
palinilap.cpp:63:43: error: 'MOD' was not declared in this scope
63 | FORN(i, 1, n) pw[i] = pw[i-1] * 311 % MOD;
| ^~~
palinilap.cpp:64:70: error: 'MOD' was not declared in this scope
64 | FORN(i, 1, n) (prefix[i] = prefix[i-1] *311 + w[i] - 'a' + 1) %= MOD;
| ^~~
palinilap.cpp:65:76: error: 'MOD' was not declared in this scope
65 | FORD(i, n, 1) (suffix[n-i+1] = suffix[n-i] * 311 + w[i] - 'a' + 1) %= MOD;
| ^~~
