预处理然后前缀和的

#include <bits/stdc++.h>
#define maxn 5010

int f[maxn][maxn], d[maxn][maxn];
int main()
{
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::string s;
    int t, l, r;
    std::cin >> s >> t;
    for (int i = 0; i < s.size(); i++)
        f[i][i] = d[i][i] = 1;
    int n = s.size();
    for (int l = 1; l < n - 1; l++)
        for (int i = 0; i + l < n; i++)
        {
            int j = i + l;
            if (l == 1 && s[i] == s[j])
                f[i][j] = 1, d[i][j] = 3;
            else if (s[i] == s[j] && f[i + 1][j - 1] == 1)
                f[i][j] = 1;
        }

    // for (int i = 0; i < n; i++)
    // {
    //     for (int j = 0; j < n; j++)
    //         std::cout << f[i][j] << " ";
    //     std::cout << std::endl;
    // }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            d[i][j] = d[i - 1][j] + d[i][j - 1] - d[i - 1][j - 1] + f[i - 1][j - 1];
    // for (int i = 0; i < n; i++)
    // {
    //     for (int j = 0; j < n; j++)
    //         std::cout << d[i][j] << " ";
    //     std::cout << std::endl;
    // }
    while (t--)
    {
        std::cin >> l >> r;
        std::cout << d[r][r] - d[l][l] + f[l][l] << std::endl;
    }
    return 0;
}