Question

这是一种算法，我试图使用本地搜索来解决2-SAT问题。但是，我似乎遇到了分段错误：11。问题从for ( int i =0; i<upper_limit; i++)之后的主代码开始。

如何解决此错误？

#include <fstream>
#include <iostream>
#include<math.h>
#include <map>
#include <vector>
#include <set>
#include <random>
#include <math.h>

using namespace std;

bool check_clause(short &logic,bool x1,bool x2)
{
    switch(logic)
        {
            case 0:
                return ( (not x1) or (not x2) ); 
            case 1:
                return ( (not x1) or x2 );
                break;
            case 2:
                return ( x1 or (not x2) );
                break;
            case 3:
                return( x1 or x2 );
                break;
        }
        return false;
}

int check_logic(vector<int> & elem)
{
    short logic=0;
    //Creating logic flag to construct teach clause Eg. x or !x2 = (10)(bin)= (2)(decimal)
    for(int j =1; j>=0;j--)
    {
        if (elem[j]>0)
        {
            logic+=pow(2,1-j);
        }
    }
    return logic;
}

vector <int> check_assignment(map <int,bool> &assignment,map <int, vector<int> > &data)
{   int count=0;
    vector <int> unsatisfied;
    for (auto elem: data)
    {   //Variables for both vertex indices for clause and the logic flag
        int first_vertex=abs(elem.second[0]);
        int second_vertex=abs(elem.second[1]);
        short logic=check_logic(elem.second);

        //Retrieving randomly generated boolean variables for first and second vertex of current clause
        bool x1 = assignment[first_vertex];
        bool x2 = assignment[second_vertex];
        bool answer=check_clause(logic,x1,x2);

        if (answer==false)
        {
            unsatisfied.push_back(count);
        }
        count+=1;

    }

    return unsatisfied;
}

bool isKeyInMap(int number, map <int,vector<int> > & dictionary)
{
    if (dictionary.find(number)==dictionary.end())
    {
        return false;
    }
    else
    {
        return true;
    }
}

int main()
{
    random_device rd;
    mt19937 gen(rd());
    uniform_int_distribution<> dis(0,1);
    map <int, vector<int> > data;
    map<int,vector<int> >::iterator it;
    vector<int> row(2,0);   
    ifstream file_read("2sat1.txt");
    int a;
    int n;
    file_read>>n;
    cout<<n<<endl;
    map <int, vector<int> > positives;
    map <int, vector<int> > negatives;
    int count=0;

    while (file_read>>a)
    {
        row[0]=a;
        file_read>>a;
        row[1]=a;
        data[count].insert(data[count].end(),row.begin(),row.end());


        for (auto element: row)
        {
            if (element<0)
                {
                    negatives[ -element ].push_back(count);
                }
            else 
            {
                positives[ element ].push_back(count);
            }


        }


        count++;
    }


    int n_rows=positives.size();
    int incl_count=0;

    vector <int> deletionList;
    set <int> inclset;
    // cout<<isKeyInMap(200001,positives)<<endl;

    for (int i =1; i<=n;i++)
    {
        bool pos_entry=isKeyInMap(i,positives);
        bool neg_entry=isKeyInMap(i,negatives);

        if ( pos_entry != neg_entry )
        {
            if (pos_entry==true)
            {
                deletionList.insert(deletionList.end(),positives[i].begin(),positives[i].end());
            }
            else
            {
                deletionList.insert(deletionList.end(),negatives[i].begin(),negatives[i].end());
            }
        }
        else if ((pos_entry==neg_entry) and (pos_entry==true))
        {

            inclset.insert(i);
        }


    }
    cout<<"Inclusion set size: "<<inclset.size()<<endl;
    int incl_size=inclset.size();

    set <int> deletionSet(deletionList.begin(),deletionList.end());
    cout<<"Set Size: "<<deletionSet.size()<<endl;
    // sort(deletionList.begin(),deletionList.end());

    for (auto i=deletionSet.rbegin(); i!=deletionSet.rend();++i)
    {

        for (auto item: data[*i])
        {
            cout<<item<<" ";
        }
        it=data.find(*i);
        if (it!=data.end())
        {
            data.erase(it);
        }
        else
        {
            cout<<"Not found!"<<endl;
        }


    }
    cout<<data.size()<<endl;


    map <int,bool> assignment;
    int upper_limit= (int) ceil ( log2(incl_size) );
    long local_iter_size= 2*pow(incl_size,2);

    for (auto elem: inclset)
    {
        assignment[elem]=(bool) dis(gen);
    }




    for ( int i =0; i<upper_limit; i++)
    {

        for (auto elem: inclset)
        {
            assignment[elem]= (bool) dis(gen);

        }

        for (auto elem: assignment)
        {
            cout<<elem.first<<":"<<elem.second<<endl;
        }
        cout<<"Size of assignment: "<<assignment.size()<<endl;

        for (int j=0; j<local_iter_size; j++)
        {
            cout<<"Okay "<<j<<endl;
            vector <int> unsatisfied;
            unsatisfied = check_assignment(assignment,data);

            if (unsatisfied.empty())
            {
                cout<<"Yay, we win!";
                return 0;
            }

            int pick_random= unsatisfied[rand()% unsatisfied.size()];
            vector <int> record= data[pick_random];
            short logic=check_logic(record);
            int first_vertex=abs(record[0]);
            int second_vertex=abs(record[1]);
            bool x1=assignment[first_vertex];
            bool x2= assignment[second_vertex];

            if (check_clause(logic,not x1,x2)==true)
            {
                assignment[first_vertex]
                = not x1;
            }
            else
            {
                assignment[second_vertex]=not x2;
            }
            cout<<"Number of unfulfilled clauses: "<<unsatisfied.size()<<endl;
        }


    }


}

Answer 1

if (answer==false)
        {
            unsatisfied.push_back(count);
        }
        count+=1;

在check_clause函数中找到的此子句有错误。我们应该推动不满足条款的密钥索引，即unsatisfied.push_back(elem.first)。由于此错误，程序尝试访问向量unsatisfied范围之外的索引。

现在，代码工作正常。

如何解决此分段错误：以下代码出现11错误？

1 个答案: