[英]Why does my c++ program crashes at with a particular input?
有些日子我正在尝试用一个程序来模拟一个非确定性有限自动机(NFA),更具体地说,是一个字符串识别器。 经过多次失败,感谢用户Konrad Rudolph ,我可以实现基于此伪代码的解决方案:
好吧,在NFA中你有一组当前状态,并且在每一步中你都会经历所有当前状态,并且对于每一个状态,你选择所有有效的转换。 这些组合集构成了您的新状态集。
最后,检查当前状态和接受状态的交集是否为非空。
在伪代码中,这看起来如下:
current = { initial }
for each char in input:
next = { }
for each state in current:
for each transition in transitions[state][char]:
next.append(target_of(transition))
current = next
if len(intersection(current, accepting)) > 0:
print "String accepted"
else:
print "String rejected"
这可以逐行转换为C ++代码。 他建议使这很简单,使用std::set<int> for the current and next sets
Herés我在c ++中的实现:
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <utility>
#include <vector>
using namespace std;
int main (){
int testCases, i, j,k, cont=1,finalStates,numberInputs,stateOrigin, stateDestination;
int numberStates, numberTransitions, initialState;
int numberFinals;
char transitionCharacter ;
set<int> current;
set<int> next;
set<int>::iterator it;
set <int> final;
set<int> the_intersection; // Destination of intersect
map<pair<int, int>, char>::iterator p;
string inputString;
typedef std::pair<int, int> trigger;
std::map<trigger, char> transitions;
map<trigger, char>::iterator r;
cin>> testCases;
for (i=0;i< testCases;i++){
final.clear();
next.clear();
current.clear();
the_intersection.clear();
transitions.clear();
cin>>numberStates>>numberTransitions>>initialState>>numberFinals;
for (j=0;j<numberFinals;j++){
cin>>finalStates;
final.insert(finalStates);
}
for (j=0; j<numberTransitions;j++){
cin>> stateOrigin>>stateDestination>>transitionCharacter;
transitions.insert(make_pair(make_pair(stateOrigin, stateDestination), transitionCharacter));
}
cin>>numberInputs;
current.insert (initialState);
cout<<"Test Case #"<<cont++<<":"<<endl;
for (j=0; j<numberInputs;j++){
current.clear();
current.insert (initialState);
the_intersection.clear();
cin>> inputString;
cout<<inputString<<" ";
/// ///////////////Konrad Rudolph's solution /////////////////
for (k=0; k<inputString.size();k++){
next.clear();
for (it = current.begin(); it!=current.end(); it++){
for (r =transitions.begin(); r!=transitions.end(); r++){
if ( ((*r).first.first == *it) && ( (*r).second == inputString[k] ) ){
next.insert((*r).first.second);
}
}
current = next;
}
}
std::set_intersection(current.begin(), current.end(), final.begin(), final.end(), std::inserter(the_intersection, the_intersection.end()));
if (the_intersection.empty()){
cout<<"Rejected"<<endl;
}else {
cout<<"Acepted"<<endl;
}
/// ///////////////////////////////////////////////////////
}
cout<<endl;
}
return 0;
}
我有这个输入:
1
6 8 0 2
2
5
0 0 a
0 1 a
1 1 b
1 2 c
1 3 c
3 4 d
4 4 d
4 5 d
5
aaabcccc
aabbbbcdc
abbcdddcc
abc
acdddddd
预期的产出是:
Test Case #1:
aaabcccc Rejected
aabbbbcdc Rejected
abbcdddcc Rejected
abc Acepted
acdddddd Acepted
但是,我的代码产生输出:
Test Case #1:
aaabcccc Rejected
aabbbbcdc Rejected
abbcdddcc Rejected
abc Acepted
acdddddd
对于测试用例的最后一个字符串,程序什么都不做,只是不停止运行。 我的问题是为什么我的程序崩溃了这个特定的输入。 我在JFlap中设计了相同的自动机NFA,并识别出最后一个输入
acdddddd
。
(0, a) = 1
(1, c) = 2
(2, d) = 3
(3, d) = 4
(4, d) = 4
(4, d) = 4
(4, d) = 4
(4, d) = 5
我在执行代码时遇到了什么错误?
你想做;
for each char in input:
next = { }
for each state in current:
for each transition in transitions[state][char]:
next.append(target_of(transition))
current = next
但你正在做的是;
for each char in input:
next = { }
for each state in current:
for each transition in transitions[state][char]:
next.append(target_of(transition))
current = next
微妙,但重新分配电流同时循环它可能会导致你的挂起,绝对不会给出所需的结果。
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