Array indexes
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i need help with writing a c code lets say i have an array[5] i need to make a new array that gets the indexes of the array[5] from the maximum number to the minimum one. example {2,5,1,8,4} my new array of indexes will be (counting from ZERO) {3,1,4,0,2} i though of sorting it and save the indexes in a temporary array or something but it didnt work any ideas how can i solve this ?
Hi, the normal approach to sort an array value[] without moving its content is this: - create an index array, initialized to 0...N-1 - implement whatever sort algorithm you like on that array, except, rather than comparing index[i] and index[j], compare value[index[i]] and value[index[j]] and move the content of index[] around as a result of the sorting steps. :)
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i need help with writing a c code lets say i have an array[5] i need to make a new array that gets the indexes of the array[5] from the maximum number to the minimum one. example {2,5,1,8,4} my new array of indexes will be (counting from ZERO) {3,1,4,0,2} i though of sorting it and save the indexes in a temporary array or something but it didnt work any ideas how can i solve this ?
thanks for your replies guys i appreciate it ive tried this code.. it may look bad lol but i'll appreciate it a lot if someone can tell me how to correct it
int a\[\] = {2,1,5,4,7};//assuming that the size of array is 5 -> initializing it from 0-4
int index[] = {0,1,2,3,4};
int i,j,temp;for(int i=0; i<5; i++) { for(int j=0; j<5-1; j++) { if(a\[index\[j\]\]>a\[index\[j+1\]\]) { temp = index\[a\[j+1\]\]; index\[a\[j+1\]\] = index\[a\[j\]\]; index\[a\[j\]\] = temp; } } }thanks ;)
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thanks for your replies guys i appreciate it ive tried this code.. it may look bad lol but i'll appreciate it a lot if someone can tell me how to correct it
int a\[\] = {2,1,5,4,7};//assuming that the size of array is 5 -> initializing it from 0-4
int index[] = {0,1,2,3,4};
int i,j,temp;for(int i=0; i<5; i++) { for(int j=0; j<5-1; j++) { if(a\[index\[j\]\]>a\[index\[j+1\]\]) { temp = index\[a\[j+1\]\]; index\[a\[j+1\]\] = index\[a\[j\]\]; index\[a\[j\]\] = temp; } } }thanks ;)
Farraj wrote:
temp = index[a[j+1]]; index[a[j+1]] = index[a[j]]; index[a[j]] = temp;
you should drop all the a[]'s here, you really want to swap two index entries, no more, no less. :)
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modified on Sunday, April 11, 2010 9:47 AM
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i need help with writing a c code lets say i have an array[5] i need to make a new array that gets the indexes of the array[5] from the maximum number to the minimum one. example {2,5,1,8,4} my new array of indexes will be (counting from ZERO) {3,1,4,0,2} i though of sorting it and save the indexes in a temporary array or something but it didnt work any ideas how can i solve this ?
i believe this will do it[^]...
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Farraj wrote:
temp = index[a[j+1]]; index[a[j+1]] = index[a[j]]; index[a[j]] = temp;
you should drop all the a[]'s here, you really want to swap two index entries, no more, no less. :)
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
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We all depend on the beast below.
modified on Sunday, April 11, 2010 9:47 AM
thank you. i've got it working but the array is sorted from the minimum index to the maximum, how can i fix it the oppisite way? this is the code so far..
if(a\[j\]>a\[j+1\]) { temp = index\[j+1\]; index\[j+1\] = index\[j\]; index\[j\] = temp; }another thing.. you've mentioned something about initializing the array from 0->N-1, ive done that while i know what size my array is. what if the size is unknown N, how can i initialize it to be from 0 to N-1? should i make another loop to initialize it or there is some other way? Thanks a lot for everyone's help ;)
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thank you. i've got it working but the array is sorted from the minimum index to the maximum, how can i fix it the oppisite way? this is the code so far..
if(a\[j\]>a\[j+1\]) { temp = index\[j+1\]; index\[j+1\] = index\[j\]; index\[j\] = temp; }another thing.. you've mentioned something about initializing the array from 0->N-1, ive done that while i know what size my array is. what if the size is unknown N, how can i initialize it to be from 0 to N-1? should i make another loop to initialize it or there is some other way? Thanks a lot for everyone's help ;)
Farraj wrote:
what if the size is unknown N
you create and initialize the index array after the value array is known, so you do know N.
Farraj wrote:
how can i fix it the oppisite way?
if you were to understand what you have done so far, you wouldn't be asking such question... :(
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Farraj wrote:
what if the size is unknown N
you create and initialize the index array after the value array is known, so you do know N.
Farraj wrote:
how can i fix it the oppisite way?
if you were to understand what you have done so far, you wouldn't be asking such question... :(
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
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I did understand Luc thank you for your help this is my code for now
#include <stdio.h>
#define N 5
void main()
{int a\[N\]; int index\[N\]; int i,j,temp; int count=0; for(i=0; i<N; i++) { //set the values of array a\[\] scanf("%d",&a\[i\]); //initializing the index\[\] array from 0->N-1 index\[i\]=count++; } for(i=0; i<N; i++) { for(j=0; j<N-1; j++) { if(a\[j\]>a\[j+1\]) { temp = index\[j+1\]; index\[j+1\] = index\[j\]; index\[j\] = temp; } } }for (i = 0; i < N; ++i)
{
printf("%d ",index[i]);
}
flushall();
getchar();}
i think it should work perfectly, its just it doesnt !! though it looks exactly how it should be can u run it and tell me where is the problem please? Thanks.
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I did understand Luc thank you for your help this is my code for now
#include <stdio.h>
#define N 5
void main()
{int a\[N\]; int index\[N\]; int i,j,temp; int count=0; for(i=0; i<N; i++) { //set the values of array a\[\] scanf("%d",&a\[i\]); //initializing the index\[\] array from 0->N-1 index\[i\]=count++; } for(i=0; i<N; i++) { for(j=0; j<N-1; j++) { if(a\[j\]>a\[j+1\]) { temp = index\[j+1\]; index\[j+1\] = index\[j\]; index\[j\] = temp; } } }for (i = 0; i < N; ++i)
{
printf("%d ",index[i]);
}
flushall();
getchar();}
i think it should work perfectly, its just it doesnt !! though it looks exactly how it should be can u run it and tell me where is the problem please? Thanks.
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I did understand Luc thank you for your help this is my code for now
#include <stdio.h>
#define N 5
void main()
{int a\[N\]; int index\[N\]; int i,j,temp; int count=0; for(i=0; i<N; i++) { //set the values of array a\[\] scanf("%d",&a\[i\]); //initializing the index\[\] array from 0->N-1 index\[i\]=count++; } for(i=0; i<N; i++) { for(j=0; j<N-1; j++) { if(a\[j\]>a\[j+1\]) { temp = index\[j+1\]; index\[j+1\] = index\[j\]; index\[j\] = temp; } } }for (i = 0; i < N; ++i)
{
printf("%d ",index[i]);
}
flushall();
getchar();}
i think it should work perfectly, its just it doesnt !! though it looks exactly how it should be can u run it and tell me where is the problem please? Thanks.
Farraj wrote:
if(a[j]>a[j+1])
is obviously wrong. you need to look at the a value "through the index array". try
if(a[index[j]]>a[index[j+1]])
that is what you have to pay for the fact that you never actually move the a values around; all you do is change the index values. You have had the test correct a while ago... :)
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
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We all depend on the beast below.
-
Farraj wrote:
if(a[j]>a[j+1])
is obviously wrong. you need to look at the a value "through the index array". try
if(a[index[j]]>a[index[j+1]])
that is what you have to pay for the fact that you never actually move the a values around; all you do is change the index values. You have had the test correct a while ago... :)
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
Prolific encyclopedia fixture proof-reader browser patron addict?
We all depend on the beast below.