1930

class Solution {
public:
    int countPalindromicSubsequence(string s) {
        // vector<vector<int>> v(26);
        // for(int i=0;i<s.size();i++){
        //     v[s[i]-'a'].push_back(i);
        // }
        // int c=0;
        // for(vector<int> i:v){
        //     vector<int> d=i;
        //     int t=d[0];
        //     int m=d[d.size()-1];
        //     for(auto j:v){
        //         if(j!=i){
        //             vector<int> p=j;
        //             for(int i=0;i<p.size();i++){
        //                 if(p[i]>t && p[i]<m){
        //                     c++;
        //                     break;
        //                 }
        //             }


        //             }
        //         }
        //     }
        //     return c;
     
        vector<vector<int>> positions(26);

        // Storing positions of each character in the string
        for (int i = 0; i < s.size(); ++i) {
            positions[s[i] - 'a'].push_back(i);
        }

        int count = 0;

        // Iterating over characters
        for (int i = 0; i < 26; ++i) {
            vector<int> char_positions = positions[i];

            // Checking if the character occurs at least twice
            if (char_positions.size() > 1) {
                int start = char_positions.front();
                int end = char_positions.back();

                // Checking distinct characters between start and end positions
                set<char> distinct_chars(s.begin() + start + 1, s.begin() + end);

                // Incrementing count by the number of distinct characters
                count += distinct_chars.size();
            }
        }

        return count;
    }
};