把原问题转化成的N叉树的问题（只需记录当前节点的父结点是谁？）

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;
string name;

struct Person {
  string name;
  Person* parent;
  Person(string _name) : name(_name), parent(nullptr) {};
  ~Person() {};
};

unordered_map<string, Person*> humans;
vector<string> queries;

Person* find(const string& name) {
  Person* p = humans[name];
  if (!p) {
    p = new Person(name);
    humans[name] = p;
  }
  return p;
}

// 找爷爷 （一直向上找，直到没有parent）
string findGrandFather(const string& name) {
  Person* p = find(name);
  while (p->parent) p = p->parent;
  return p->name;
}

int main(void) {
  Person *parent, *p;
  parent = p = nullptr;
  while (cin >> name, name != "$") {
    char op = name[0];
    name = name.substr(1);
    switch (op) {
      case '#': parent = find(name); break;
      case '+': p = find(name); p->parent = parent; break;
      case '?': queries.emplace_back(name); break;
    }
  }

  for (const auto& name : queries)
    cout << name << ' ' << findGrandFather(name) << endl;
}