Tree Locking Protocol

class LockingTree {
    private:
    vector<int>parent;
    map<int,vector<int>>children;
    map<int,int>lockby;
public:
    LockingTree(vector<int>& p):parent(p) {
        
        for(int i = 0;i<p.size();++i){
            children[p[i]].push_back(i);
        }
    }
    
    bool lock(int num, int user) {
        if(lockby.find(num)!=lockby.end())
            return false;
        lockby[num]=user;
        return true;
    }
    
    bool unlock(int num, int user) {
        if(lockby.find(num)==lockby.end())
            return false;
        if(lockby[num]!=user)
            return false;
        lockby.erase(num);
        return true;
    }
    bool checkparent(int num){
        if(num==-1)return false;
        
        if(lockby.find(num)!=lockby.end())
            return true;
        return checkparent(parent[num]);
    }
    bool checkchild(int num){
        bool flag = false;
        if(lockby.find(num)!=lockby.end())
            flag = true;
        for(auto ch:children[num])
            flag |= checkchild(ch);
        return flag;
    }
    void unlockchild(int num){
        for(auto ch:children[num]){
            lockby.erase(ch);
            unlockchild(ch);
        }
    }
    bool upgrade(int num, int user) {
        if(lockby.find(num)!=lockby.end())
            return false;
        if(checkchild(num) and !checkparent(num))
        {
            unlockchild(num);
            lockby[num]=user;
            return true;
        }
        return false;
    }
};

/**
 * Your LockingTree object will be instantiated and called as such:
 * LockingTree* obj = new LockingTree(parent);
 * bool param_1 = obj->lock(num,user);
 * bool param_2 = obj->unlock(num,user);
 * bool param_3 = obj->upgrade(num,user);
 */