CareerCup

Assuming character groups of size 2.
Assuming string will not begin with '|' as character group in that case is undefined.

Idea is to reverse the string normally once and in the second pass, identify the character groups(of size three) and reverse them alone to restore their original order.

#include<stdio.h>
#include<string.h>

int getLength(char* input)
{
	int length = 0;
	
	while(*input)
	{
		length++;
		input++;
	}
	return length;
}

//Normal string reversal
void reverseStringRegular(char* input, int begin, int end)
{	
	if(begin >= end) return;
	
	int i = begin, j = end;
	while(i <= j)
	{
		char ch = input[i];
		input[i] = input[j];
		input[j] = ch;
		
		i++; j--;
	}
}

//Find character groups and reverse them again to get original order
void detectGroupsAndReverse(char* input)
{
	int i = 0;
	
	while(input[i] != '\0')
	{
		if(input[i] == '|')
		{
			reverseStringRegular(input, i-1, i+1);
			i = i+2;
			continue;
		}
		i++;
	}
}

void reverseStringByGroup(char* input)
{
	int stringLength = getLength(input);
	if(input[0] == '|' || input[stringLength - 1] == '|')
	{
		printf("Invalid string. Character Grouping failed\n");
		return;
	}
	reverseStringRegular(input,0, stringLength - 1);
	detectGroupsAndReverse(input);
}

int main()
{
	char input[] = "dar|dkik i|s n|ice";
	printf("Input String: %s\n", input);
	
	reverseStringByGroup(input);
	printf("String Reversed: %s\n", input);
}

Execute at www .ideone. com / f5Yfx

nice solution!

Almost, but not quite. At the link at ideone you've given:

Input String: dar|dkik i|s n|ice
String Reversed: ecn|i i|s kikr|dad