Find the minimum time in HH:MM:SS format given a string of 6 digits.

minimum_clock_time.cpp

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
char strings[1000][7];
int comparator(const void *p, const void *q) 
{
    int l = *((char *)p);
    int r = *((char *)q); 
    return (l - r);
}
void swap(char *x, char *y)
{
    char temp;
    temp = *x;
    *x = *y;
    *y = temp;
}
int findCeil (char str[], char first, int l, int h)
{
    int ceilIndex = l;
 
    for (int i = l+1; i <= h; i++)
      if (str[i] > first && str[i] < str[ceilIndex])
            ceilIndex = i;
 
    return ceilIndex;
}

int ptr = 0;
void sortedPermutations ( char str[] )
{
    int size = strlen(str);
 
    qsort( str, size, sizeof( str[0] ), comparator );
 
    bool isFinished = false;
    while ( ! isFinished )
    {
        strcpy(strings[ptr++],str);
 
        int i;
        for ( i = size - 2; i >= 0; --i )
           if (str[i] < str[i+1])
              break;
 
        if ( i == -1 )
            isFinished = true;
        else
        {
            int ceilIndex = findCeil( str, str[i], i + 1, size - 1 );
 
            swap( &str[i], &str[ceilIndex] );
 
            qsort( str + i + 1, size - i - 1, sizeof(str[0]), comparator );
        }
    }
}
 
int hour_check(char *hr){
	if((hr[0]=='0'||hr[0]=='1')&&(hr[1]>='0'&&hr[1]<='9')){
		return 1;
	}else if(hr[0]=='2'&&hr[1]>='0'&&hr[1]<='3'){
		return 1;
	}else {
		return 0;
	}
	return 0;
}
int minute_check(char *hr){
	if((hr[2]>='0'&&hr[2]<='5') && (hr[3]>='0'&&hr[3]<='9')){
		return 1;
	}else {
		return 0;
	}
	return 0;
}
int seconds_check(char *hr){
	if((hr[4]>='0'&&hr[4]<='5') && (hr[5]>='0'&&hr[5]<='9')){
		return 1;
	}else {
		return 0;
	}
	return 0;
}
int main()
{
    char str[] = "000789";
    int n = strlen(str);
    sortedPermutations(str);
    int len = ptr;
    for(int t = 0; t<len; t++){
    	if(hour_check(strings[t]) && minute_check(strings[t]) && seconds_check(strings[t])){
    	    	printf("%s\n", strings[t]);
    	    	return 0;
    	}else{
    		continue;
    	}
    }
    return 0;
}