Question

我正在尝试实现Merge-sort，这是我的代码：

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
using namespace std;
void merge_inplace (int *elem , int *axu, int lo, int mid, int hi)
{
    int i =lo;
    int j= mid +1;
    for (int k=lo;k<hi; k++)
    {
        axu[k]=elem[k];
    }
    for(int k=lo; k<hi;k++)
    {
        if(i> mid)
            elem[k]=axu[i++];
        else if(j> hi)
            elem[k]=axu[j++];
        else if (axu[i]<axu[j])
            elem[k]= axu[i++];
        else elem[k]= axu[j++];
    }
}

void mergesort(int *elem ,int *axu, int lo,int hi)
{
    if(hi<=lo) return;
    int mid = lo + (hi-lo)/2;
    mergesort(elem,axu, lo, mid);
    mergesort(elem,axu, mid+1,hi);
    merge_inplace(elem,axu,lo, mid, hi );
}

int main()
{
    ifstream in_file ;
    ofstream out_file;
    int size =0;
    int element;
    int* elem;
    in_file.open("in_file.txt");
    if (!in_file )perror ("Error openning file");


    in_file >> size;
    elem = new int[size];

    for (int i=0; i<size;i++)
    {
        in_file >> elem[i];
    }

    int * axu = new int [size];
    mergesort (elem,axu,0,size-1);

    out_file.open("out_file.txt");

    if (out_file.fail())
    {
        printf( "Error opening file for output.\n");

        return 0;
    }
    for (int i=0; i < size; i++)
    {
        out_file << elem[i];
    }
    out_file.close();
    return 0;
}

“out_file.txt”中程序的输出如下：

-842150451-842150451-842150451-842150451-842150451-842150451-33686019-1414812757-84215045110

调试后我发现当合并函数返回时，元素数组会破坏并使值错误

我的输入文件包含（每行一个整数）：

10 9 7 5 1 8 3 6 4 2 10

Answer 1

合并排序和错误的一些错误将辅助初始化转移到合并排序功能

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
using namespace std;
void merge_inplace (int *elem , int *axu, int lo, int mid, int hi)
{

    int i =lo;
    int j= mid +1;
    for (int k=0;k<=hi; k++)  // <------------- transfer initialization into the merge 
    {
        axu[k]=elem[k];
    }
    for(int k=lo; k<=hi;k++)
    {
        if(i> mid)
            elem[k]=axu[j++];   // <----------------- i<--->j
        else if(j> hi)
            elem[k]=axu[i++];   // <------------------ i<--->j
        else if (axu[i]<axu[j])
            elem[k]= axu[i++];
        else elem[k]= axu[j++];
    }
}
void mergesort_book(int *elem ,int *axu, int lo,int hi)
{
    if(hi<=lo) return;
    int mid = lo + (hi-lo)/2;
    mergesort_book(elem,axu, lo, mid);
    mergesort_book(elem,axu, mid+1,hi);
    merge_inplace(elem,axu,lo, mid, hi );
}
//static void merge(vector <int> elements, )
int main()
{
        ifstream in_file ;
        ofstream out_file;
        int size =0;
        int element;
        int* elem;
        in_file.open("in_file.txt");
        if (!in_file )perror ("Error openning file");


                    in_file >> size;
                    elem = new int[size];

        for (int i=0; i<size;i++)
        {
            in_file >> elem[i];
        }

        int * axu = new int [size];

        mergesort_book (elem,axu,0,size-1);

        out_file.open("out_file.txt");        

   if (out_file.fail())         
   {
      printf( "Error opening file for output.\n");

      return 0;
   }
        for (int i=0 ; i < size; i++)
        {
            //out_file << elem[i]; 
            printf("%d\n", elem[i]);
        }
        out_file.close();
return 0;
}

合并排序做错了答案

1 个答案: