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/*
Challenge 012
Challenge #2
Write a script that finds the common directory path, given a collection of
paths and directory separator. For example, if the following paths are
supplied.
/a/b/c/d
/a/b/cd
/a/b/cc
/a/b/c/d/e
and the path separator is /. Your script should return /a/b as common
directory path.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
void* check_mem(void* p) {
if (!p) {
fputs("Out of memory", stderr);
exit(EXIT_FAILURE);
}
return p;
}
char* common_path(char sep, char* paths[], int num_paths) {
const char* p0 = paths[0];
const char* end_common = paths[0];
while (true) {
const char* p1 = strchr(p0, sep);
if (p1 == NULL)
p1 = p0 + strlen(p0);
for (int i = 1; i < num_paths; i++) {
const char* q0 = paths[i] + (p0 - paths[0]);
const char* q1 = strchr(q0, sep);
if (q1 == NULL)
q1 = q0 + strlen(q0);
if (q1 - q0 != p1 - p0 ||
strncmp(paths[0], paths[i], p1 - paths[0]) != 0)
goto failed;
}
end_common = p1;
p0 = p1 + 1;
}
failed:
{
char* ret = check_mem(strdup(paths[0]));
ret[end_common - paths[0]] = '\0'; // truncate
return ret;
}
}
int main(int argc, char* argv[]) {
if (argc != 1) {
fputs("usage: ch-2", stderr);
return EXIT_FAILURE;
}
char line[BUFSIZ];
if (!gets(line)) {
fputs("expected separator from input", stderr);
return EXIT_FAILURE;
}
char sep = line[0];
char** paths = NULL;
int num_paths = 0;
while (gets(line)) {
num_paths++;
paths = check_mem(realloc(paths, num_paths * sizeof(char**)));
paths[num_paths - 1] = check_mem(strdup(line));
}
if (num_paths == 0) {
fputs("expected paths from input", stderr);
return EXIT_FAILURE;
}
char* common = common_path(sep, paths, num_paths);
printf("%s\n", common);
free(common);
for (int i = 0; i < num_paths; i++)
free(paths[i]);
free(paths);
}
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