Possibility of finishing all courses given pre-requisites

• Time : $O(v + e)$
• Space : $O(v + e)$

int Solution::solve(int A, vector<int> &B, vector<int> &C) {
    unordered_map<int,int> ind;
    unordered_map<int,vector<int>> adj;
    for(int i = 0; i < B.size(); i++) {
        ind[C[i]]++;
        ind[B[i]] += 0;
        adj[B[i]].push_back(C[i]);
    }
    queue<int> q;
    for(auto [k,v] : ind) {
        if(v == 0) q.push(k);
    }
    while(q.size()) {
        int u = q.front(); q.pop();
        for(auto v : adj[u]) {
            if(--ind[v] == 0) {
                q.push(v);
            }
        }
    }
    for(auto [k,v] : ind) if(v) return false;
    
    return true;
}