题解 | #密码截取#

#include <bits/stdc++.h>
using namespace std;
pair<int, int> expandOfString(string& s, int left, int right){
    while(left >= 0 && right < s.size() && s[left] == s[right]){
        left--;
        right++;
    }
    return {left + 1, right - 1};
}
int main() {
    string s;
    cin >> s;
    int begin = 0, end = 0;
    for(int i = 0; i < s.size(); ++i){
        auto [left1, right1] = expandOfString(s, i, i);
        auto [left2, right2] = expandOfString(s, i, i + 1);
        if(right1 - left1 > end - begin){
            begin = left1;
            end = right1;
        }
        if(right2 - left2 > end - begin){
            begin = left2;
            end = right2;
        }
    }
    cout << end - begin + 1 << endl;
    return 0;
}
// 64 位输出请用 printf("%lld")