Find Sequences of any range - c

Question

Given an array of numbers, print the each and every range available.
For example
Array : 9, 3, 5, 7, 4, 8, 1
Output: 1, 3-5, 7-9
Note: Please execute this problem without using an additional array.
How do i proceed?
*
#include<stdio.h>
int main()
{
int a[]={9,8,8,7,6,5,14};
int n= sizeof(a) / sizeof(a[0]);
int i,j;
int temp;
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(a[i]>a[j])
{
temp=a[i];
a[i]=a[j];
a[j]=temp;
}
}
}
}
*
1st i will sort in ascending order, i don't know what to do next?
P.S : I am coding this in C.

Answer 1

The next step is to identify sequences. Try the following loop (not fully debugged):
first= next= a[0];
for (i=1; i<n; i++) {
if (a[i] > next+1) {
if (next>first)
printf("%d-%d,", first, next);
else printf("%d,", first);
first= next= a[i];
}
else next++;
}

Answer 2

If you may to change the original array that is if you may to sort it then the program can look like
#include <stdlib.h>
#include <stdio.h>
int cmp( const void *lhs, const void *rhs )
{
int a = *( const int * )lhs;
int b = *( const int * )rhs;
return ( b < a ) - ( a < b );
}
int main()
{
int a[] = { 9, 8, 8, 7, 6, 5, 14 };
const size_t N = sizeof( a ) / sizeof( *a );
qsort( a, N, sizeof( int ), cmp );
/*
for ( size_t i = 0; i < N; i++ ) printf( "%d ", a[i] );
printf( "\n" );
*/
int *p = a;
int *start = a, *end = a;
do
{
if ( ++p == a + N || *p != *end + 1 )
{
printf( "{ %d", *start );
start == end ? printf( " }\n" ) : printf( ", %d }\n", *end );
start = end = p;
}
else
{
end = p;
}
} while ( p != a + N );
}
The program output is
{ 5, 8 }
{ 8, 9 }
{ 14 }

Answer 3

I wrote a simple, readable function for you, take a look:
void printRange(int sortedArray[], int len) {
int i, current, next, printStart, printEnd, startIndex = 0;
bool print = false;
for (i = 0; i < len; i++) {
printStart = sortedArray[startIndex];
printEnd = sortedArray[i];
current = sortedArray[i];
if(i < len -1) {
next = sortedArray[i + 1];
} else
next = current;
if (next - current != 1) {
startIndex = i + 1;
print = true;
}
if (print) {
if (printStart - printEnd == 0) {
printf("%d,", printStart);
} else {
printf("%d-%d,", printStart, printEnd);
}
print = false;
}
}
}
Run live.
Note, for good understanding variable current is declared whereas current and printEnd is same. You may replace current by printEnd.

Answer 4

There are already some pretty good answers for this task in here but maybe the sorting part in the beginning is worth to talk a little bit more about. Especially if you need something like that in school, university or in a job interview.
The easiest sorting technique/algorithm would be something like BubbleSort which can easily be implemented with 2 for loops.
void BubbleSort (int a[], int length)
{
int i, j, temp;
for (i = 0; i < length; i++)
{
for (j = 0; j < length - i - 1; j++)
{
if (a[j + 1] < a[j])
{
temp = a[j];
a[j] = a[j + 1];
a[j + 1] = temp;
}
}
}
}
Source and more information
The best way of sorting such arrays with integers (or any kind of number) is QuickSort. The algorithm is pretty advanced but if you watch a good video on Youtube or read this article you definitely know how it works.
void quick(int array[], int start, int end){
if(start < end){
int l=start+1, r=end, p = array[start];
while(l<r){
if(array[l] <= p)
l++;
else if(array[r] >= p)
r--;
else
swap(array[l],array[r]);
}
if(array[l] < p){
swap(array[l],array[start]);
l--;
}
else{
l--;
swap(array[l],array[start]);
}
quick(array, start, l);
quick(array, r, end);
}
}
Source and more information
Note: QuickSort uses a technique called recursion. If you are not familiar which that you can have a look here:
In computer science, recursion is a method of solving a problem where the solution depends on solutions to smaller instances of the same problem. Such problems can generally be solved by iteration, but this needs to identify and index the smaller instances at programming time. Recursion solves such recursive problems by using functions that call themselves from within their own code. The approach can be applied to many types of problems, and recursion is one of the central ideas of computer science.
Source and more information