6-15 Iterative Mergesort（25 分）

6-15 Iterative Mergesort（25 分）

How would you implement mergesort without using recursion?

The idea of iterative mergesort is to start from N sorted sublists of length 1, and each time to merge a pair of adjacent sublists until one sorted list is obtained. You are supposed to implement the key function of merging.

Format of functions:

void merge_pass( ElementType list[], ElementType sorted[], int N, int length );

The function merge_pass performs one pass of the merge sort that merges adjacent pairs of sublists from list into sorted. N is the number of elements in the list and length is the length of the sublists.

Sample program of judge:

#include 

#define ElementType int
#define MAXN 100

void merge_pass( ElementType list[], ElementType sorted[], int N, int length );

void output( ElementType list[], int N )
{
    int i;
    for (i=0; i

Sample Input:

10
8 7 9 2 3 5 1 6 4 0

Sample Output:

7 8 2 9 3 5 1 6 0 4 
2 7 8 9 1 3 5 6 0 4 
1 2 3 5 6 7 8 9 0 4 
0 1 2 3 4 5 6 7 8 9 
0 1 2 3 4 5 6 7 8 9

void merge_pass(ElementType list[], ElementType sorted[], int N, int length)
{
int Ptr3 = 0;
int i;
for (i = 0; i <= N-2*length; i=i+2*length) {
int Ptr1 = i, Ptr2 = i + length;
while (Ptr1 < i + length && Ptr2 < i + 2 * length) {
if (list[Ptr1] < list[Ptr2])
sorted[Ptr3++] = list[Ptr1++];
else
sorted[Ptr3++] = list[Ptr2++];
}
if (Ptr1 == i + length && Ptr2 != i + 2 * length)
while (Ptr2 sorted[Ptr3++] = list[Ptr2++];
if (Ptr2 == i + 2 * length && Ptr1 != i + length)
while (Ptr1 sorted[Ptr3++] = list[Ptr1++];
}
if (i + length < N) {
int Ptr1 = i, Ptr2 = i + length;
while (Ptr1 < i + length && Ptr2 < N) {
if (list[Ptr1] < list[Ptr2])
sorted[Ptr3++] = list[Ptr1++];
else
sorted[Ptr3++] = list[Ptr2++];
}
if (Ptr1 == i + length && Ptr2 != N)
while (Ptr2 < i + 2 * length)
sorted[Ptr3++] = list[Ptr2++];
if (Ptr2 == N && Ptr1 != i + length)
while (Ptr1 < i + length)
sorted[Ptr3++] = list[Ptr1++];
}
else
for (int j = i; j < N; j++)
sorted[j] = list[j];
}