老菜鸟……请各路大神不小心翻到牌的时候抽空教一哈,
个人思路是先判断文法式子是否可推导,定义一维数组存放被|分开的字符串,但是写不出来,求源代码QAQ
使用C/C++编程实现消除左递归
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- fcyh 2017-11-07 12:01关注
#include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <string> #include <vector> #include <queue> #include <cctype> #include <map> #include <set> #define MAX 507 using namespace std; class WF { public: string left; set<string> right; WF ( const string& temp ) { left = temp; right.clear(); } void print ( ) { printf ( "%s::=" , left.c_str() ); set<string>::iterator it = right.begin(); printf ( "%s" , it->c_str()); it++; for ( ; it!= right.end() ; it++ ) printf ( "|%s" , it->c_str() ); puts(""); } void insert ( const string& temp ) { right.insert(temp); } }; map<string,int> VN_dic; vector<WF> VN_set; string start; bool used[MAX]; //消除间接左递归 void remove1 ( ) { for ( int i = 0 ; i < VN_set.size() ; i++ ) for ( int j = 0 ; j < i ; j++ ) { vector<string> cont; set<string>& right1 = VN_set[i].right; set<string>& right2 = VN_set[j].right; char ch = VN_set[j].left[0]; set<string>::iterator it1 = right1.begin(); set<string>::iterator it2; for ( ; it1 != right1.end() ; it1++ ) if ( it1->at(0) == ch ) for ( it2 = right2.begin() ; it2 != right2.end() ; it2++ ) cont.push_back ( *it2 + it1->substr(1) ); int nn = right1.size(); while ( nn-- ) { if ( right1.begin()->at(0) == ch ) right1.erase ( right1.begin() ); else { cont.push_back ( *right1.begin() ); right1.erase ( right1.begin() ); } } for ( int i = 0 ; i < cont.size() ; i++ ) right1.insert ( cont[i] ); } #define DEBUG #ifdef DEBUG for ( int i = 0 ; i < VN_set.size() ; i++ ) VN_set[i].print(); #endif } //消除直接左递归 void remove2 ( ) { for ( int i = 0 ; i < VN_set.size() ; i++ ) { char ch = VN_set[i].left[0]; set<string>& temp = VN_set[i].right; set<string>::iterator it = temp.begin(); string tt = VN_set[i].left.substr(0,1)+"\'"; bool flag = true; for ( ; it != temp.end() ; it++ ) if ( it->at(0) == ch ) { VN_set.push_back ( WF(tt)); VN_dic[tt] = VN_set.size(); flag = false; break; } int x = VN_dic[tt]-1; if ( flag ) continue; vector<string> cont; set<string>& ss = VN_set[x].right; ss.insert ( "~" ); while (!temp.empty()) { if ( temp.begin()->at(0) == ch ) ss.insert(temp.begin()->substr(1)+tt); else { //cout << "YES : " << temp.begin()->substr(1)+tt; cont.push_back (temp.begin()->substr(0)+tt); } temp.erase(temp.begin()); } puts (""); for ( int i = 0 ; i < cont.size() ; i++ ) { //cout << cont[i] << endl; temp.insert ( cont[i] ); } } #define DEBUG #ifdef DEBUG for ( int i = 0 ; i < VN_set.size() ; i++ ) VN_set[i].print(); #endif } void dfs ( int x ) { if ( used[x] ) return; used[x] = 1; set<string>::iterator it = VN_set[x].right.begin(); for ( ; it != VN_set[x].right.end(); it++ ) for ( int i = 0 ; i < it->length() ; i++ ) if ( isupper(it->at(i)) ) { if ( it->length() > i+1 && it->at(i+1) == '\'' ) dfs ( VN_dic[it->substr(i,2)]-1 ); else dfs ( VN_dic[it->substr(i,1)]-1 ); } } //化简 void simplify ( ) { memset ( used , 0 , sizeof ( used ) ); int x = VN_dic[start]-1; dfs ( x ); puts ( "finish" ); vector<WF> res; for ( int i = 0 ; i < VN_set.size() ; i++ ) if ( used[i] ) res.push_back ( VN_set[i] ); VN_set.clear(); VN_set = res; } void print () { puts("**********消除左递归后的结果********"); for ( int i = 0 ; i < VN_set.size() ; i++ ) VN_set[i].print(); puts(""); } int main ( ) { char buf[MAX]; int n; VN_dic.clear(); VN_set.clear(); start="S"; puts ("请输入文法G[S]的产生式数量"); while ( ~scanf ("%d" , &n ) ) { scanf ( "%d" , &n ); while ( n-- ) { scanf ( "%s" , buf ); int len = strlen ( buf ),i; for ( i = 0 ; i < len ; i++ ) if ( buf[i] == ':' ) { buf[i] = 0; break; } string temp = buf; if ( !VN_dic[temp] ) { VN_set.push_back ( WF(temp)); VN_dic[temp] = VN_set.size(); } int x = VN_dic[temp]-1; temp = buf+i+3; //cout <<"the right : " << temp << endl; VN_set[x].insert(temp); } remove1(); remove2(); simplify(); print(); //puts ("请输入文法G[S]的产生式数量"); } }
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