Question

以下是使用动态编程算法解决0-1背包问题的C ++程序。 Keep是一个2D数组，用于确定项目是否包含在最大答案中（使用1和0）。程序编译但运行时出现以下错误：抛出'std :: length_error'的实例后终止调用 what（）：basic_string :: _ S_create 中止

这是我的代码：

#include <iostream>
#include <fstream>
#include <cstring>
#include <vector>
using namespace std;      

static ifstream fr;
static vector<int> stolen_Profit;
static vector<int> stolen_Weight;
static vector<string> stolen_Name;

   /**class for item object*/
   class Item
    {
public:
    /**constructor that will get information from the file*/
    Item()
    {
        fr>>name>>p>>w;
        r=p/w;
    }

    /**@return the name of the item object*/
    string getName()
    {return name;}

    /**@return the weight of the item object*/
    int getWeight()
    {return w;}

    /**@return the weight of the item object*/
    int getProfit()
    {return p;}

    /**@return the weight of the item object*/
    double getRatio()
    {return r;}

private:
    string name;
    double r;
    int w, p;
};

int max(int a, int b)
{
    int max=a;
    if (b>a)
    {max=b;}
    return max;
}

void finditems(int remainingweight, int item, int **Keep, int Weight[], int     Profit[], string Name[])
{   
    if (item!=0)
    {
        if(Keep[item][remainingweight]==1)
        {
            stolen_Weight.push_back(Weight[item]);
            stolen_Profit.push_back(Profit[item]);
            stolen_Name.push_back(Name[item]);
            remainingweight=remainingweight-Weight[item];
            item=item-1;
            finditems(remainingweight,item, Keep, Weight, Profit, Name);

            //add the item to stolen

        } 

        if(Keep[item][remainingweight]==0)
        {
            item=item-1;
            finditems(remainingweight,item, Keep, Weight, Profit, Name);
        }
    }
    else return;
}

void knapsack(int n, int W, int Weight[], int Profit[], string Name[], int *P[], int *Keep[])
{
    //set all values in the 0 row to 0
    for(int i=0; i<=W; i++)
    {
        P[0][i]=0;
        Keep[0][i]=0;
    }

    for(int i=0; i<=n; i++)
    {
        //set all values in the 0 weight column to 0
        P[i][0]=0;
        Keep[i][0]=0;

    for (int j=1; j<=W; j++)
    {
        if (Weight[i]<=j)
        {
            P[i][j]= max(P[i-1][j], Profit[i] + P[i-1][j-Weight[i]]);
            if (P[i][j]==P[i-1][j])
            {Keep[i][j]=0;}
            else 
            Keep[i][j]=1;
        }
        else 
        P[i][j]=P[i-1][j];
        Keep[i][j]=0;
    }
}

finditems(W, n, Keep, Weight, Profit, Name);

int totalweight=0;
/**print out information to output file*/
ofstream fw;
fw.open("outputp1.txt");
//# of items in solution
cout<<stolen_Name.size()<<endl;
//total weight
for(int i=0; i<stolen_Weight.size(); i++)
{
    totalweight=totalweight+stolen_Weight[i];
}
cout<<totalweight<<endl;

//total profit
cout<<P[n][W]<<endl;
//print out the information of each item
for(int i=0; i<stolen_Name.size(); i++)
{cout<< stolen_Name[i]<<" "<< stolen_Profit[i] << " "<< stolen_Weight[i]<<endl;}

fw.close();

}

int main()
{
    int n, W;
    fr.open("inputp1.txt");
    fr>>n>>W; 

/**create an array of Items objects based on n*/
Item tosteal[n];

int *Profit=new int[n+1];
int *Weight=new int[n+1];
string *Name=new string[n+1];
for (int i=0; i<=n; i++)
{
    if (i==0)
    {
        Profit[i]=0;
        Weight[i]=0;
        Name[i]="";
    }
    else
    Profit[i]= tosteal[i-1].getProfit();
    Weight[i]= tosteal[i-1].getWeight();
    Name[i]= tosteal[i-1].getName();
}

int **P= new int *[n+1];
int **Keep= new int *[n+1];
for (int i=0; i<=n; i++ )
{
    P[i]=new int [W];
    Keep[i]=new int [W];
}

fr.close();
knapsack(n, W, Weight, Profit, Name, P, Keep);

cout <<"Solution to 0-1 Knapsack Problem written to file."<<endl;

//garbage collection
for (int i=0; i<=n;i++)
{
    delete P[i];
    delete Keep[i];
}   
delete P;
delete Keep;
delete Weight;
delete Profit;
delete Name;
//delete stolen_Name;
//delete stolen_Profit;
//delete stolen_Weight;
}

Answer 1

确保变量n是您期望的数字（尝试cout << "n = " << n << " W = " << W << '\n';进行调试）
看起来您可能希望在其自己的块中使用else语句
最好的办法是在调试器中运行代码。你在用Linux吗？如果是，请运行带有gdb [your-command]的命令，然后键入run，然后当它崩溃时键入where以获取堆栈跟踪。它应该告诉你造成崩溃的线路。

程序在运行时中止，0-1背包

1 个答案: