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