归并排序的问题

[djjlove_2008]

#include <iostream>
using namespace std;

void Merge(int a[], int tmp[], int lPos, int rPos, int rEnd)
{
int lEnd = rPos - 1;
int tmpPos = lPos;

while(lPos <= lEnd && rPos <= rEnd)
{
if(a[lPos] <= a[rPos])
tmp[tmpPos++] = a[lPos++];
else
tmp[tmpPos++] = a[rPos++];
}

while(lPos <= lEnd)
tmp[tmpPos++] = a[lPos++];

while(rPos <= rEnd)
tmp[tmpPos++] = a[rPos++];

int numElements = rEnd - lPos + 1;
for(int i; i < numElements; i++)
a[i] = tmp[i];

}

void Msort(int a[], int tmp[], int low, int high)
{
if(low < high)
return;
int middle = (low + high) / 2;

Msort(a, tmp, low, middle);
Msort(a, tmp, (middle + 1), high);
Merge(a, tmp, low, (middle + 1), high);
}

void MergeSort(int a[], int len)
{
int *tmp = new int[len];
if(tmp != NULL)
{
Msort(a, tmp, 0, len - 1);
delete []tmp;
}
}

int main()
{
int a[] = {1, 3, 4, 2, 8, 5, 6};
MergeSort(a, 7);

cout << "The sorted array is:" << endl;
for(int i = 0; i < sizeof(a) / sizeof(a[0]); i++)
cout << a[i] << " ";
cout << endl;

system("pause");
return 0;
}

这道归并排序为为什么不想作用了?

[AlanBruce]

UP

UP

[macrojj]

for(int i; i < numElements; i++)
a[i] = tmp[i];


int i=0

谢谢

[走好每一步]

楼上正解。
楼主对while循环用的不错，不过尽量使用就近原则。
void Merge(int a[], int tmp[], int lPos, int rPos, int rEnd)；
这个接口设计有问题，temp数组应该在此函数内开辟，毕竟参数少点更清晰。
输入：数组首地址，排序好的两部分下标。
输出：排序数组。

而不是
输入：数组首地址，采用一个temp数组放？？，同上
输出：同上。

暴露自己的实现只会让使用者迷惑。

[djjlove_2008]

不是这样的,这样实现只是为了她的通用性更好,这道程序我写了半天,按照书上的提示的思想,写的.
#include <iostream>
using namespace std;

void Merge(int a[], int tmp[], int lPos, int rPos, int rEnd)
{
int lEnd = rPos - 1;
int tmpPos = lPos;

while(lPos <= lEnd && rPos <= rEnd)
{
if(a[lPos] <= a[rPos])
tmp[tmpPos++] = a[lPos++];
else
tmp[tmpPos++] = a[rPos++];
}

while(lPos <= lEnd)
tmp[tmpPos++] = a[lPos++];

while(rPos <= rEnd)
tmp[tmpPos++] = a[rPos++];

int numElements = rEnd - lPos + 1;
for(int i = 0; i < numElements; i++)
a[i] = tmp[i];

}

void Msort(int a[], int tmp[], int low, int high)
{
if(low < high)
return;
int middle = (low + high) / 2;

Msort(a, tmp, low, middle);
Msort(a, tmp, (middle + 1), high);
Merge(a, tmp, low, (middle + 1), high);
}

void MergeSort(int a[], int len)
{
int *tmp = new int[len];
if(tmp != NULL)
{
Msort(a, tmp, 0, len - 1);
delete []tmp;
}
}

int main()
{
int a[] = {1, 3, 4, 2, 8, 5, 6};
MergeSort(a, 7);

cout << "The sorted array is:" << endl;
for(int i = 0; i < sizeof(a) / sizeof(a[0]); i++)
cout << a[i] << " ";
cout << endl;

system("pause");
return 0;
}
这样改过之后仍然有问题存在.排序的问题仍然不存在,你们运行试试..

[djjlove_2008]

//通用性很好的一道归并排序，妙哉
#include <iostream>
using namespace std;

void Merge(int a[], int tmp[], int lPos, int rPos, int rEnd)
{
int i, lEnd, NumElements, tmpPos;
lEnd = rPos - 1;
tmpPos = lPos;
NumElements = rEnd - lPos + 1;

while(lPos <= lEnd && rPos <= rEnd)
{
if(a[lPos] <= a[rPos])
tmp[tmpPos++] = a[lPos++];
else
tmp[tmpPos++] = a[rPos++];
}

while(lPos <= lEnd)
tmp[tmpPos++] = a[lPos++];
while(rPos <= rEnd)
tmp[tmpPos++] = a[rPos++];

for(i = 0; i < NumElements; i++, rEnd--)
a[rEnd] = tmp[rEnd];
}

void msort(int a[], int tmp[], int low, int high)
{
if(low >= high)
return;
int middle = (low + high) / 2;
msort(a, tmp, low, middle);
msort(a, tmp, (middle + 1), high);
Merge(a, tmp, low, (middle + 1), high);
}

void merge_sort(int a[], int len)
{
int *tmp = NULL;
tmp = new int[len];
if(tmp != NULL)
{
msort(a, tmp, 0, len - 1);
delete []tmp;
}
}

void print_array(int a[], int len)
{
for(int i = 0; i < len; i++)
cout<<a[i]<<" ";
cout<<endl;
}

int main()
{
int a[8] = {8, 6, 1, 3, 5, 2, 7, 4};
cout<<"The original array:"<<endl;
print_array(a, 8);
merge_sort(a, 8);
cout<<"The sorted array:"<<endl;
print_array(a, 8);

system("pause");
return 0;
}


这样改过之后仍然存在,大家看看有什么区别了,呵呵,,,共同进步...

[djjlove_2008]

谢谢各位