3839. Number of Prefix Connected Groups

You are given an array of strings words and an integer k.

Two words a and b at distinct indices are prefix-connected if a[0..k-1] == b[0..k-1].

A connected group is a set of words such that each pair of words is prefix-connected.

Return the number of connected groups that contain at least two words, formed from the given words.

Note:

• Words with length less than k cannot join any group and are ignored.
• Duplicate strings are treated as separate words.

class Solution {
public:
    int prefixConnected(vector<string>& words, int k) {
        unordered_map<string,int> freq;
        for(auto& w : words) {
            if(w.length() < k) continue;
            else freq[w.substr(0,k)]++;
        }
        int res = 0;
        for(auto& [k,v] : freq) res += (v >= 2);
        return res;
    }
};