3447. Assign Elements to Groups with Constraints

You are given an integer array groups, where groups[i] represents the size of the ith group. You are also given an integer array elements.

Your task is to assign one element to each group based on the following rules:

• An element j can be assigned to a group i if groups[i] is divisible by elements[j].
• If there are multiple elements that can be assigned, assign the element with the smallest index j.
• If no element satisfies the condition for a group, assign -1 to that group.

Return an integer array assigned, where assigned[i] is the index of the element chosen for group i, or -1 if no suitable element exists.

Note: An element may be assigned to more than one group.

class Solution {
public:
    vector<int> assignElements(vector<int>& groups, vector<int>& elements) {
        unordered_set<int> E,G(begin(groups), end(groups));
        vector<vector<int>> rgroups(101010);
        vector<int> res(groups.size(), -1);
        for(int i = 0; i < groups.size(); i++) rgroups[groups[i]].push_back(i);
        for(int i = 0; i < elements.size(); i++) {
            int e = elements[i];
            if(E.count(e)) continue;
            for(int j = e; j <= 1e5; j += e) {
                if(!G.count(j)) continue;
                while(rgroups[j].size()) {
                    auto idx = rgroups[j].back(); rgroups[j].pop_back();
                    res[idx] = i;
                }
                G.erase(j);
            }
            E.insert(e);
        }

        return res;
    }
};