JavaScript solution for https://www.geeksforgeeks.org/find-same-contacts-in-a-list-of-contacts/

find-same-contacts-in-a-list-of-contacts.js

(() => {
    'use strict';

    /**
     * get unique contacts
     * @param {object} contacts
     * @return {Array.<Array.<string>>}
     */
    const getUniqueContacts = (contacts) => {

        const keys = Object.keys(contacts);

        if(keys.length <= 0) return [];

        const result = [];

        //create an adjacency list
        const adjacencyList = {};

        for(let i=0; i<keys.length; i++){
            const key = keys[i];
            adjacencyList[key] = new Set();
        }

        for(let i=0; i<keys.length; i++){

            const key1 = keys[i];
            const emailsList1 = contacts[key1];

            for(let j=i+1; j<keys.length; j++){

                const key2 = keys[j];
                const emailsList2 = contacts[key2];

                const set = new Set(emailsList1.concat(emailsList2));

                if(emailsList1.length + emailsList2.length > set.size){

                    //contains common email
                    adjacencyList[key1].add(key2);
                }
            }
        }

        const visited = {};

        //BFS to find connected components
        for(let i=0; i<keys.length; i++){

            if(visited[keys[i]]) continue;

            //find connected components
            const queue = [keys[i]];
            const res = [];

            while(queue.length > 0){

                const item = queue.shift();
                res.push(item);
                visited[item] = true;

                const children = adjacencyList[item];
                children.forEach(child => {
                    if(!visited[child]){
                        queue.push(child);
                    }
                });
            }

            result.push(res);
        }

        return result;
    };

    const contacts = {
        c1: ['[email protected]', '[email protected]'],
        c2: ['[email protected]'],
        c3: ['[email protected]', '[email protected]'],
        c4: ['[email protected]'],
        c5: ['[email protected]'],
        c6: ['[email protected]', '[email protected]']
    };

    console.log(getUniqueContacts(contacts));

    /*
    should return:
    [(c1, c3, c5), (c2), (c4, c6) ]
     */
})();