2_str_maxlenoc.c

//solution 1, the slim version: 

#include <unistd.h>

int len(char *str) 
{
	int len = 0;
	while(str[len] != '\0')
		len++;
	return (len);
}

int     ft_strstr(char *str1, char *str2, int start, int end) 
{
    for (int i = 0, beg = start; str1[i]; i++, start = beg)
    {
        for (;str1[i] == str2[start] && start < end; i++, start++) 
            ;
        if (start == end)
            return (1);
        else
            i -= start - beg;
    }
    return (0);
}
int		main(int ac, char **av)
{
	if (ac >= 2)
	{
		int	min_len = 2147483647;
		int min_i = 1; 
		for (int i = 1; i < ac; i++)
		{
			int clen = len(av[i]);
			if (clen < min_len)
			{	
				min_len = clen;
				min_i = i; 
			}
		}
		for(int i = 0, match, offset = min_len; i < min_len ; i++, offset--)
			for(int j = 0; j <= i; j++) 
			{
				match = 0;
				for (int avi = 1; avi < ac; avi++)
					if (avi != min_i && ft_strstr(av[avi], av[min_i], j, j + offset))
						match++;
				if(match == ac - 2)
				{
					for (int i = j; i < j + offset; i++)
						write(1, &(av[min_i][i]), 1);
					write(1, "\n", 1);
					return (0);
				}
			}
	}
	write(1, "\n", 1);
	return (0);
}



// solution 2:

#include <unistd.h>
#include <stdlib.h>
#define SIZE 256
#define pc(c) write(1, &c, 1);

void	ps(char *str)
{
	int i = 0;
	while (str[i])
		pc(str[i++]);
}

int ft_strlen(char *str)
{
 	int len = 0;
 	while (str[len])
 		len++;
 	return (len);   
}

int 	cmp(char *s1, char *s2)
{
	int i = 0;
	while (s1[i] == s2[i])
	{
		if (s1[i] == '\0')
			return (0);
		i++;
	}
	return (unsigned char)s1[i] - (unsigned char)s2[i];
}

char 	**str_permu(char str[], int n)  
{
	char **per;
	int len = (n * (n + 1)) / 2; 
	int col, row = 0;

	per = (char **)malloc(sizeof(char *) * len);
	for (int len = 1; len <= n; len++)
	{
		for (int i = 0; i <= n - len; i++)
		{
			int j = i + len - 1;
			per[row]= (char *)malloc(i + 2);
			per[row][i + 1] = '\0';
	      	col = 0;
			for (int k = i; k <= j; k++)
				per[row][col++] = str[k];
			row++;
		}
	}
    return (per);
} 
/* yes, it's freaking O(n)*/
int 	match(char *pat, char *str)
{
	int lp = ft_strlen(pat);
	int ls = ft_strlen(str);
	char p[SIZE] = {0}, s[SIZE] = {0};

	for (int i = 0; i < lp; i++)
	{
		p[i] = pat[i];
		s[i] = str[i];
	}
	for (int i = lp; i <= ls; i++)
	{
		if (cmp(p, s + i - lp) == 0)
			return (1);
		s[i] = str[i];
	}
	return (0);
}

int main(int ac, char **av)
{
	if (ac <= 2)
	{
		if (ac == 2)
			ps(av[1]);
		ps("\n");
		return (0);
	}
	else
	{
		char	**pat;
		int 	len = ft_strlen(av[1]);
		int 	av_i = 1;
		char 	*arr_match;
 
		pat = str_permu(av[1], len);
		len = (len * (len + 1)) / 2;
	   	arr_match = (char *)malloc(len);
		for (int i = 0; i < len; i++)
			arr_match[i] = 1;
		while (av_i < ac)
		{
			for (int i = 0; i < len; i++)
				if (!match(pat[i], av[av_i]))
					arr_match[i] = 0;
			av_i++;
		}
		for (int i = len - 1; i >= 0; i--)
		{
			if (arr_match[i])
			{
				int p_len = ft_strlen(pat[i]);
				for (int j = i; j >= 0 && ft_strlen(pat[j]) == p_len; j--)
					if (j < i && arr_match[j])
						i = j;
				ps(pat[i]);
				ps("\n");
				break ;
			}
		}
	   	free(arr_match);
	   	free(pat);
	}
	return (0);
}