我正在编写一个实现快速排序,插入排序和合并排序的程序。我可以得到所有工作,除了合并排序,我无法弄清楚为什么。请忽略操作和比较变量。它们是如此我可以分析不同输入文件的运行时和操作数。此代码以这种方式从main通过类对象运行:
Merge testobj13(test_Med[0], 100);
testobj13.merCall();
testobj13.display();
对于排序列表,类保持列表排序,对于反转列表,除了第一个和最后一个值之外,列表仍然保持相反,对于随机列表,我看不到输出和原始输入之间的任何模式。在等待答案的时候,我会尝试回答其他问题。任何批评都是受欢迎的,即使它只是关于我的代码或语法与这里的整体问题无关。我根据我的算法类编写的sudo代码编写了这段代码,所以我很难在这里找出错误。
# include <iostream>
# include <stdio.h>
# include <stdlib.h>
using namespace std;
class Merge{
public:
int comparisons, operations, middle, i, j, k, size;
int *myArray, *c;
Merge::~Merge(){
myArray = 0;
delete myArray;
}
Merge::Merge(int a [], int n) {
size= n;
myArray= new int[size];
comparisons = 0, operations = 0, middle = 0, i = 0, j = 0, k = 0;
for(int x = 0; x < size; x++){
myArray[x] = a[x];
}
}
void combine(int arr [], int first, int middle, int last){
i = first, j = middle + 1, k = first; operations = operations + 3;
c = new int[last + 1]; operations ++;
while( (i <= middle) && (j <= last) ){
comparisons++;operations++;
if(arr[i] <= arr[j]){operations++;
c[k] = arr[i]; operations++;
i++; operations++;
}
else{
c[k] = arr[j]; operations++;
j++; operations++;
}
k++; operations++;
}
while(i <= middle){operations++;
c[k] = arr[i]; operations++;
i++; operations++;
k++; operations++;
}
while(j <= last){operations++;
c[k] = arr[j]; operations++;
j++; operations++;
k++; operations++;
}
for(int k = first; k <= last; k++){operations++;
arr[k] = c[k]; operations++;
}
c = 0;
delete c;
}
void mer(int arr [], int first, int last){
operations++; //for the comparison in the following if statement
if ( first < last ){
middle = (first + last) / 2; operations++;
mer(arr, first, middle); operations++;
mer(arr, middle + 1, last); operations++;
combine(arr, first, middle, last); operations++;
}
}
void merCall(){
mer(myArray, 0, size - 1);
}
void display(){
cout << "The array after going through Merge Sort: " ;
for(int x = 0; x < size; x++){
cout << endl << myArray[x];
}
cout << endl << "Number of operations :" << operations << "\t comparisons: " << comparisons << endl;
}
};
答案 0 :(得分:1)
您的“中间”变量在递归期间被覆盖,因为它是类成员而不是局部变量:
middle = (first + last) / 2; operations++;
// This is going to affect middle
mer(arr, first, middle); operations++;
// So this isn't going to work on the range you think it is.
mer(arr, middle + 1, last); operations++;
combine(arr, first, middle, last); operations++;
最好将middle声明为局部变量:
int middle = (first + last) / 2; operations++;
mer(arr, first, middle); operations++;
mer(arr, middle + 1, last); operations++;
combine(arr, first, middle, last); operations++;