PAT1040

简单dp，有O(n)做法，这里O(n^2)水过

#include <fstream>
#include <iostream>
#include <vector>
#include <string>

using namespace std;

#define OJ

#ifdef OJ
#define fin cin
#else
ifstream fin("in.data");
#endif

int dp(const string &str){
    int size = str.size();
    vector<vector<bool> > f(size, vector<bool>(size, false));

    for (int i = 0; i < size; i++)
        f[i][i] = true;

    int res = 1;

    for (int len = 2; len <= size; len++){
        for (int s = 0; s <= size - len; s++){
            int e = s + len - 1;
            if (str[s] == str[e] && ((s + 1 > e - 1) || (f[s + 1][e - 1]))){
                f[s][e] = true;
                if (len > res)
                    res = len;
            }
        }
    }

    return res;
}

int main(){
    string str;
    getline(cin, str);

    cout << dp(str) << endl;

    return 0;
}