题解 | #密码截取#

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

int main() {
    string str;
    cin >> str;
    int max_len = 0;
    vector<vector<bool>> dp(str.length(), vector<bool>(str.length(), false));
    for(int  right = 0; right < str.length(); right++){
        for(int left = 0; left <= right; left++){
            if(left == right) dp[right][left] = true;
            else if(right - left == 1 && str[left] == str[right]) dp[right][left] = true;
            else dp[right][left] = (str[left] == str[right] && dp[right-1][left+1]);
            if(dp[right][left]){
                max_len = max(max_len, right - left + 1);
            }
        }
    }
    cout << max_len << endl;
    return 0;
}