PAT1034

题目链接：http://pat.zju.edu.cn/contests/pat-a-practise/1034

思路：用DFS， 一次DFS遍历可得到一个连通域，用vector<string> 记录下。在判断即可，借助C++的容器，邻接表很容易实现。

#include<iostream>
#include<map>
#include<iterator>
#include<vector>
#include<string>
#include<algorithm>
using namespace std;

struct Node
{
    string head;
    int members;
};

bool comp(Node n1, Node n2)
{
    if(n1.head < n2.head)
        return true;
    else
        return false;
}

void DFS_visit(map<string, vector<string>> &gra, map<string, int> &used, 
                        vector<string> &s, string start)
{
    s.push_back(start);
    used[start] = 1;
    vector<string>::iterator iter = gra[start].begin();
    for(; iter != gra[start].end(); ++iter)
        if(used[*iter] == 0)
            DFS_visit(gra, used, s, *iter);
}

void DFS_version(map<string, int> &mem, map<string, vector<string>> &gra, 
                            map<string, int> used, int K)
{
    vector<Node> outcome;
    map<string, vector<string>>::iterator  iter= gra.begin();
    for(; iter != gra.end(); ++iter)
    {
        /*保存DFS时路径*/
        vector<string> s;
        if(used[iter->first] == 0)
        {
            /*一次DFS可得一个连通域，用s记录*/
            DFS_visit(gra, used, s, iter->first);
            if( s.size() > 2)
            {
                int relation(0);
                for(int i=0; i<s.size(); ++i)
                    relation += mem[s[i]];
                /*注意除2,因为之前mem存的是点所有边权重之和*/
                if(relation/2 > K)
                {
                    Node n; n.members = s.size();
                    int max(-1);
                    string who;
                    for(int j=0; j<s.size(); ++j)
                        if(mem[s[j]] > max)
                        {
                            max = mem[s[j]];
                            who = s[j];
                        }
                    n.head = who;
                    outcome.push_back(n);
                }
            }
        }
    }
    sort(outcome.begin(), outcome.end(), comp);
    cout<<outcome.size()<<endl;
    for(int i=0; i<outcome.size(); ++i)
        cout<<outcome[i].head<<" "<<outcome[i].members<<endl;
}

int main()
{
    int N, K;
    while(cin>>N>>K)
    {
        /*存每个点的总权重*/
        map<string, int> mem;
        /*邻接表*/
        map<string, vector<string>> gra;
        /*标记是否DFS访问过*/
        map<string, int> used;
        string s1, s2; int m;
        for(int i=0; i<N; ++i)
        {
            cin>>s1>>s2>>m;
            mem[s1]+=m;
            mem[s2]+=m;
            gra[s1].push_back(s2);
            gra[s2].push_back(s1);
            used[s1] = 0;
            used[s2] = 0;
        }
        DFS_version(mem, gra, used, K);
    }
    return 0;
}