【机试备考】Day24-first集 | map、set插入遍历

输入描述

输出描述

示例

输入

4B AA abA cA #

输出

A a c #B a c #

题解

#include <bits/stdc  .h>using namespace std;struct pro{char left;    string right;};//输出first集void print(pair<char,set<char>>p){cout<<p.first<<" ";    int empty=0;    for(auto it=p.second.begin(); it!=p.second.end(); it  )    {if(it==(--p.second.end())&&!empty)            cout<<*it;        else if(*it!='#')            cout<<*it<<" ";        else            empty=1;    }    if(empty==1)        cout<<"#";    cout<<endl;}int main(){int n;    while(cin>>n)    {map<char,set<char>>first;        vector<pro>productions;        for(int i=0; i<n; i  )        {pro p;            cin>>p.left>>p.right;            productions.push_back(p);        }        int circle=5;        while(circle--)        {for(pro p:productions)            {char r=p.right[0];                if(r>='a'&&r<='z')//X->a                {first[p.left].insert(r);                    continue;                }                else if(p.right.size()==1&&r=='#')//X->#                {first[p.left].insert('#');                    continue;                }                else if(r>='A'&&r<='Z')//X->AB                {int add=0;//添加#                    for(char t:p.right)                    {for(char nt:first[t])                        {if(nt!='#')                                first[p.left].insert(nt);                            else                                add  ;                        }                    }                    if(add==p.right.size())                        first[p.left].insert('#');                }            }        }        for_each(first.begin(), first.end(), print);//打印first集