ManacherPalindromes.cpp

/****************************************************************************

    Manacher's algorithm for finding all subpalindromes in the string.

    Based on problem L from here: http://codeforces.ru/gym/100133

****************************************************************************/

#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <cassert>
#include <utility>
#include <iomanip>

using namespace std;

const int MAXN = 105000;

string s;
int n;
int odd[MAXN], even[MAXN];          
int l, r;
long long ans;

int main() {
    assert(freopen("palindrome.in","r",stdin));
    assert(freopen("palindrome.out","w",stdout));

    getline(cin, s);
    n = (int) s.length();

    // Odd case
    l = r = -1;
    for (int i = 0; i < n; i++) {
        int cur = 1;
        if (i < r)
            cur = min(r - i + 1, odd[l + r - i]);
        while (i + cur < n && i - cur >= 0 && s[i - cur] == s[i + cur])
            cur++;
        odd[i] = cur;
        if (i + cur - 1 > r) {
            l = i - cur + 1; 
            r = i + cur - 1;
        }
    }

    // Even case 
    l = r = -1;
    for (int i = 0; i < n; i++) {
        int cur = 0;
        if (i < r) 
            cur = min(r - i + 1, even[l + r - i + 1]);
        while (i + cur < n && i - 1 - cur >= 0 && s[i - 1 - cur] == s[i + cur])
            cur++;
        even[i] = cur;
        if (i + cur - 1 > r) {
            l = i - cur;
            r = i + cur - 1;
        }
    }

    for (int i = 0; i < n; i++) {
        if (odd[i] > 1) {
            ans += odd[i] - 1;
        }
        if (even[i])    
            ans += even[i];
    }

    cout << ans << endl;

    return 0;
}