题解 | #最长回文子串#

#include <iostream>
#include <string>
using namespace std;
pair<int, int> expandAroundCenter(string &s, int left, int right){
    while(left >= 0 && right <= s.size() && s[left] == s[right]){
        left--, right++;
    }
    return {left + 1, right - 1};
}
string longestPalindrome(string& s) {
    int n = s.size();
    int begin = 0, end = 0;
    for (int i = 0; i < n; ++i) {
        auto [left1, right1] = expandAroundCenter(s, i, i);
        auto [left2, right2] = expandAroundCenter(s, i, i + 1);
        if(right1 - left1 > end - begin){
            begin = left1;
            end = right1;
        }
        if (right2 - left2 > end - begin) {
            begin = left2;
            end = right2;
        }
    }
    return s.substr(begin, end - begin + 1);
}
int main() {
    string s;
    cin >> s;
    string res = longestPalindrome(s);
    cout << res.size() << endl;

    return 0;
}
// 64 位输出请用 printf("%lld")