Longest increasing sequence in an array in C - c

Question

I want to make a program that returns me the longest increasing sequence in an array.
For example:
Input: 1, 2, 3, 2, 6, 2
Output: 1, 2, 3
Input: 4, 3, 1, 2, 4, 6, 4, 1, 5, 3, 7
Output: 1, 2, 4, 6
I managed to put together a code, but this only returns me the first sequence of consecutive, increasing numbers:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main() {
int j = 0;
int cou = 0;
int max = 0;
// c = final array; will contain the longest consecutive, increasing sequence of numbers
int c[10];
int n = 0;
int a[] = {1, 3, 5, 1, 5, 7, 8, 9, 10, 11, 12};
for (int i = 0; i < (sizeof(a)/sizeof(int)); ++i) {
if (a[i+1] > a[i])
++cou;
if (cou > max) {
max = cou;
c[j] = a[i];
c[j+1] = a[i+1];
j++;
}
if (j > n) //finding the size of my final array
n = j;
else {
cou = 0;
j = 0;
}
}
for (j = 0; j <= n; ++j)
printf("%d ",c[j]);
return 0;
}
So basically, I want the longest sequence of increasing, consecutive numbers.
Been busting my brains on this one for quite a while now, and still haven't managed to crack it open. Any help is welcome.

Answer 1

You need to iterate through array, finding sequences, and comparing their length. So, you need to remember previous length of sequence to compare. And you can't copy result to output array on the fly (if you need output array at all), because you can't predict length of next sequence. I'll better show you an example.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
int previous_len=0, start=0, c[10], len=0; //c = final array; will contain the longest consecutive, increasing sequence of numbers
int a[] = {1, 3, 5, 1, 5, 7, 8, 9, 10, 11, 12};
for (int i = 0; i < (sizeof(a)/sizeof(int)); ++i) {
if(a[i+1] > a[i]) {
len++;
if (len > previous_len) {
previous_len=len;
start=i+1-len;
}
} else {
previous_len=len;
len=0;
}
}
for(int i = 0; i <= previous_len; ++i) {
c[i]=a[start+i]; //here you can copy data to output array, if you need it
printf("%d ",c[i]); //you can output a[start+i] instead
}
return 0;
}

Answer 2

It seems to mee that you miss some curly braces:
if(a[i+1] > a[i])
{
++cou;
if (cou>max)
{max = cou;
c[j]=a[i];
c[j+1] = a[i+1];
j++;}
if (j > n) //finding the size of my final array
n=j;
}
else
{cou = 0;
j=0;}

Answer 3

I suggest breaking this down into smaller pieces.
Start with a function:
int sequenceLength(int[] array, int arrayLen, int position)
... which returns the length of the sequence beginning at position. Test it and make sure
it works. You shouldn't need help to write that.
Once you have that, you can write something like:
int longestSequence(int[] array, int arrayLen) {
int longest = 0;
int longestLen = 0;
for(int i=0; i<arrayLen; i++) {
int seqLen = sequenceLength(array, arrayLen, i);
if(seqLen > longestLen) {
longest = i;
longestLen = seqLen;
}
}
return longest;
}
Again, test this and make sure it works for all circumstances.
Finally you need a function:
printSequence(int[] array, int arrayLen, int position)
... which prints the sequence beginning at that position. Again you should be able to tackle this on your own.
Put all those together:
printSequence(array,arrayLen(longestSequence(array,arrayLen)));
It's always easiest to break a challenge like this into smaller pieces to solve it.
There may be more efficient solutions that avoid backtracking, but guessing at your level, I don't think you need to go there.
(Note: although the code here may compile, consider it as pseudocode)

Answer 4

you used a array to store the longest sequence, that made your code go wrong in printing.
And you dint use braces for if() statement that resulted in wrong sequence.
you can make the following changes to make the code work,
int main()
{int j=0, cou=0, max=0, c[10], n=0; //c = final array; will contain the longest consecutive, increasing sequence of numbers
int a[] = {1, 3, 5, 1, 5, 7, 8, 9, 10, 11, 12};
int i,k,z;
for ( k=0,i = 0; i < (sizeof(a)/sizeof(int)); ++i)
{if(a[i+1] > a[i])
{ ++cou;
if (cou>max)
{max = cou;
z=k;
}
}
else
{
k=i+1;
cou = 0;
j=0;}
}
for( j = z; j <(sizeof(a)/sizeof(int)) ; ++j)
if(a[j]<a[j+1])
printf("%d ",a[j]);
else
break;
printf("%d",a[j]);
return 0;
}