题解 | #密码截取#

#include <iostream>
using namespace std;
const int N = 3e3;
bool dp[N][N];
int main()
{
    string s;
    cin >> s;
    int n = s.size(),maxn=1;
    for (int r = 0; r < n; r++ )//右端
        for (int l = r; l >= 0; l-- )//左端
        {
            if(r == l)
                dp[r][l] = 1;
            else if (s[r]==s[l]&&(r-l == 1||dp[r-1][l+1]))
            {
                dp[r][l] = 1;
                maxn = max(maxn, r - l + 1);
            }
        }
    cout << maxn << endl;
}