我连黄题都调不出来了，好菜。

#include<bits/stdc++.h>
#define endl '\n'
typedef long long ll;
using namespace std;
char t[200005],s[20005];
unordered_map<int,int> m;
char ch;
int size,maxx,l,r,n = 1,len;
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	while((t[n] = getchar()) != EOF)n++;n--;
	for(int i = 1;i <= n;i++){
		if(isalpha(t[i]))s[++len] = tolower(t[i]),m[len] = i;
	}
	for(int i = 1;i <= len;i++){
		int j = i - 1,k = i + 1;
        while(j >= 1 && k <= len && s[j] == s[k])j--,k++;
        j++,k--;
        if(k - j + 1 > maxx)maxx = k - j + 1,l = j,r = k;
	}
	cout << r - l + 1 << endl;
	for(int i = m[l];i <= m[r];i++)cout << t[i];
}