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 listand length is the length of the sublists.
Sample program of judge:
#include <stdio.h>
#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<N; i++) printf("%d ", list[i]);
printf("\n");
}
void merge_sort( ElementType list[], int N )
{
ElementType extra[MAXN]; /* the extra space required */
int length = 1; /* current length of sublist being merged */
while( length < N ) {
merge_pass( list, extra, N, length ); /* merge list into extra */
output( extra, N );
length *= 2;
merge_pass( extra, list, N, length ); /* merge extra back to list */
output( list, N );
length *= 2;
}
}
int main()
{
int N, i;
ElementType A[MAXN];
scanf("%d", &N);
for (i=0; i<N; i++) scanf("%d", &A[i]);
merge_sort(A, N);
output(A, N);
return 0;
}
/* Your function will be put here */
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 ){
for (int i=0; i<N; i=i+2*length) {
int p1,p2,p3;
p1=i;
p2=i+length;
p3=p1;
while (p1<i+length&&p2<i+length+length&&p1<N&&p2<N) {
if(list[p1]<list[p2]){
sorted[p3]=list[p1];
p3++;
p1++;
}
else{
sorted[p3]=list[p2];
p3++;
p2++;
}
}
if(p1==i+length){
while (p2<i+length+length) {
sorted[p3]=list[p2];
p3++;
p2++;
}
}
if(p2==i+length+length){
while (p1<i+length) {
sorted[p3]=list[p1];
p3++;
p1++;
}
}
if(p2>=N){
while (p1<i+length) {
sorted[p3]=list[p1];
p3++;
p1++;
}
}
if(p1>=N){
while (p2<i+length) {
sorted[p3]=list[p2];
p3++;
p2++;
}
}
}
}