题解

动态规划会比枚举节省一点时间

C++ 代码

#include <iostream>
#include <cstring>

using namespace std;

const int N = 1010;

bool f[N][N];

int main()
{
    string s;
    getline(cin, s);
    int n = s.size();
    int max_length = 0;
    for (int i = 0; i < n; i ++ )
    {
        for (int j = 1; j <= i + 1; j ++ )
        {
            if (j == 1) f[i][j] = true;
            else if (j == 2)  {if (s[i] == s[i - 1]) f[i][j] = true;}
            else {f[i][j] = f[i - 1][j - 2] & (s[i] == s[i - j + 1]);}
            if (f[i][j] && j > max_length) max_length = j; 
        }
    }
    cout << max_length << endl;
    return 0;
}