题解 | #密码截取#

#include <iostream>
#include <stdexcept>
using namespace std;

int main() {
    string str;
    getline(cin, str);
    int maxc = 0;
    int sy;
    for (int i = 0; i < str.length(); i++) {
        sy = i;
        int pos = 1, count = 0;
        while (str[i] == str[i + pos]) {
            count += 2;
            if (i == 0 || i + pos == str.length()-1) break;
            i --;
            pos += 2;
        }
        i = sy;
        pos =1;
        maxc = max(count, maxc);
        count =0;
        while (str[i - pos] == str[i + pos]) {
            if (count == 0) count = 1;
            count += 2;
            if (i - pos <= 0 || i + pos >= str.length()-1) break;
            pos ++;
        }
        maxc = max(count, maxc);
    }
    cout << maxc << endl;
}