利用STL之map取巧做题过程

前言：这是我的一道作业题，为了减少代码量，我使用map进行数据保存，因为课堂进度并未涉及STL，所以我使用map就显得有些取巧

题目概述

main.cpp

#include <iostream>
#include "world.h"
using namespace std;
 void test_1() {
    person mike, jack, lily, carson, sucie;
    group school(0), family_1(1), family_2(1);
    // make group (act as a society)
    school.addMember(mike);
    school.addMember(jack);
    school.addMember(lily);
    family_1.addMember(mike);
    family_1.addMember(carson);
    family_2.addMember(jack);
    family_2.addMember(lily);
    family_2.addMember(sucie);
    // construct relationship in the society
    school.makeFriend(mike, jack);
    school.makeFriend(mike, lily);
    // display the society
    cout << "\n------ SCHOOL -----\n";
    school.displayGroup();
    cout << "\n------ FAMILY_1 -----\n";
    family_1.displayGroup();
    cout << "\n------ FAMILY_2 -----\n";
    family_2.displayGroup();
}
 void test_2() {
    person Baidu, Alibaba, Tencent, NTES, Kingsoft_Antivirus, _360safe;
    group BAT(1), ECommerce(1), Security(1);
    // make group (act as a society)
    BAT.addMember(Baidu);
    BAT.addMember(Alibaba);
    BAT.addMember(Tencent);
    ECommerce.addMember(Baidu);
    ECommerce.addMember(Alibaba);
    ECommerce.addMember(Tencent);
    ECommerce.addMember(NTES);
    Security.addMember(Kingsoft_Antivirus);
    Security.addMember(_360safe);
    // display the society
    cout << "\n------ BAT -----\n";
    BAT.displayGroup();
    cout << "\n------ ECommerce -----\n";
    ECommerce.displayGroup();
    cout << "\n------ Security -----\n";
    Security.displayGroup();
}
 void test_3() {
    person p0, p1, p2, p3, p4;
    group g0(0), g1(0), g2(1);
    // make group (act as a society)
    g0.addMember(p0);
    g0.addMember(p1);
    g0.addMember(p2);
    g1.addMember(p0);
    g1.addMember(p3);
    g2.addMember(p3);
    g2.addMember(p4);
    // construct relationship in the society
    g1.makeFriend(p0, p3);
    g2.breakRelation(p3, p4);
    g0.deleteMember(p2);
    // display the society
    cout << "\n------ G0 -----\n";
    g0.displayGroup();
    cout << "\n------ G1 -----\n";
    g1.displayGroup();
    cout << "\n------ G2 -----\n";
    g2.displayGroup();
}
 void test_4() {
    person p[50];
    group g0(0), g1(1);
    int p_count;
    cin >> p_count;
    // make group (act as a society)
    for (int i = 0; i < p_count/2; i++)
        g0.addMember(p[i]);
    for (int i = p_count/2; i < p_count; i++)
        g1.addMember(p[i]);
    // construct relationship in the society
    for (int i = 0; i < p_count/5; i += 2)
        g0.makeFriend(p[i], p[i+1]);
    for (int i = p_count/2; i < p_count*3/4-1; i += 2)
        g1.breakRelation(p[i], p[i+1]);
    for (int i = p_count/4; i < p_count/2; i++)
        g0.deleteMember(p[i]);
    for (int i = p_count*3/4; i < p_count; i++)
        g1.deleteMember(p[i]);
    // display the society
    cout << "\n------ G0 -----\n";
    g0.displayGroup();
    cout << "\n------ G1 -----\n";
    g1.displayGroup();
}
 int main() {
    int test_id;
    cin >> test_id;
    switch (test_id) {
        case 1:
        test_1();
        break;
        case 2:
        test_2();
        break;
        case 3:
        test_3();
        break;
        case 4:
        test_4();
        break;
        default:
        cout << "wrong input\n";
    }
    return 0;
}
 /* ---------- structure for 'world.h' ----------
 * define the struct and the class functions by yourself #(^_^)#
 * the member function is not complete, add something as you need
 struct person;
 class group {
    void displayGroup();
    bool addMember(person &p);
    bool deleteMember(person &p);
    bool makeFriend(person &p1, person &p2);
    bool breakRelation(person &p1, person &p2);
};
 */

思路

group的private成员显然需要一个容器保存每一个加进来的person，且每一个person，都需要一个容器保存他的friends，起初我是将这个容器放在了person的类定义里，但是测试时发现这样不同group类型对象中的person的friends是一样的。所以需要把friends也放进group中。
至此问题就简化成，需要一个容器保存对象，而每个对象又有自己的保存其他对象的容器，于是我想到了std::map，将person::id作为map::key_type，并使用vector<int>保存每个friends的id。通过std::map自带的接口以及<algorithm>中的泛型算法，题目便简化了很多。

world.h实现

#ifndef WORLD_H
#define WORLD_H
#include <vector>
#include <map>
#include <iostream>
#include <algorithm>
using namespace std;
static int num = 0;
struct person {
  int id;
  person(): id(num) {
    ++num;
  }
};
class group {
  private:
    map<int, vector<int>> members;
    bool known;
  public:
    group(int i): known(i) {}
    void displayGroup();
    bool addMember(person &p);
    bool deleteMember(person &p);
    bool makeFriend(person &p1, person &p2);
    bool breakRelation(person &p1, person &p2);
};
bool group::addMember(person &p) {
  if (members.find(p.id) == members.end() && p.id < 9900) {
    vector<int> temp;
    members.insert(pair<int, vector<int>>(p.id, temp));
    if (known) {
      for (auto &a: members) {
        if (a.first != p.id) {
          a.second.push_back(p.id);
          members[p.id].push_back(a.first);
        }
      }
    }
    return true;
  }
  return false;
}
bool group::deleteMember(person &p) {
  if (members.find(p.id) != members.end()) {
    members.erase(p.id);
    return true;
  }
  return false;
}
bool group::makeFriend(person &p1, person &p2) {
  if (members.find(p1.id) != members.end() && members.find(p2.id) != members.end()) {
    members[p1.id].push_back(p2.id);
    members[p2.id].push_back(p1.id);
    return true;
  }
  return false;
}
bool group::breakRelation(person &p1, person &p2) {
  vector<int>::iterator a = find(members[p1.id].begin(), members[p1.id].end(), p2.id);
  vector<int>::iterator b = find(members[p2.id].begin(), members[p2.id].end(), p1.id);
  if (members.find(p1.id) != members.end() && members.find(p2.id) != members.end() &&
      a != members[p1.id].end() && b != members[p2.id].end()) {
    members[p1.id].erase(a);
    members[p2.id].erase(b);
    return true;
  }
  return false;
}
void group::displayGroup() {
  for (auto &m: members) {
    cout << "Person_" << m.first << ": ";
    if (!m.second.size())
      cout << "null";
    for (int i = 0; i < m.second.size(); ++i) {
      cout << m.second[i];
      cout << ((i + 1 < m.second.size()) ? ", " : "");
    }
    cout << endl;
  }
}
#endif

当然，代码可能还能进一步简化， 此处不作深入。

Reference：www.cplusplus.com