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/* vi: set sw=4 ts=4: */
/*
* tsort implementation for busybox
*
* public domain -- David Leonard, 2022
*/
//config:config TSORT
//config: bool "tsort (0.7 kb)"
//config: default y
//config: help
//config: tsort performs a topological sort.
//applet:IF_TSORT(APPLET(tsort, BB_DIR_USR_BIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_TSORT) += tsort.o
/* BB_AUDIT SUSv3 compliant */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tsort.html */
//usage:#define tsort_trivial_usage
//usage: "[FILE]"
//usage:#define tsort_full_usage "\n\n"
//usage: "Topological sort"
//usage:#define tsort_example_usage
//usage: "$ echo -e \"a b\\nb c\" | tsort\n"
//usage: "a\n"
//usage: "b\n"
//usage: "c\n"
#include "libbb.h"
#include "common_bufsiz.h"
struct node {
unsigned in_count;
unsigned out_count;
struct node **out;
char name[1];
};
struct globals {
struct node **nodes;
unsigned nodes_len;
};
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
setup_common_bufsiz(); \
BUILD_BUG_ON(sizeof(G) > COMMON_BUFSIZE); \
G.nodes = NULL; \
G.nodes_len = 0; \
} while (0)
static struct node *
get_node(const char *name)
{
struct node *n;
unsigned a = 0;
unsigned b = G.nodes_len;
/* Binary search for name */
while (a != b) {
unsigned m = (a + b) / 2;
int cmp = strcmp(name, G.nodes[m]->name);
if (cmp == 0)
return G.nodes[m]; /* found */
if (cmp < 0) {
b = m;
} else {
a = m + 1;
}
}
/* Allocate new node */
n = xzalloc(sizeof(*n) + strlen(name));
//n->in_count = 0;
//n->out_count = 0;
//n->out = NULL;
strcpy(n->name, name);
/* Insert to maintain sort */
G.nodes = xrealloc(G.nodes, (G.nodes_len + 1) * sizeof(*G.nodes));
memmove(&G.nodes[a + 1], &G.nodes[a],
(G.nodes_len - a) * sizeof(*G.nodes));
G.nodes[a] = n;
G.nodes_len++;
return n;
}
static void
add_edge(struct node *a, struct node *b)
{
a->out = xrealloc_vector(a->out, 6, a->out_count);
a->out[a->out_count++] = b;
b->in_count++;
}
int tsort_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tsort_main(int argc UNUSED_PARAM, char **argv)
{
char *line;
size_t linesz;
ssize_t len;
struct node *a;
int cycles;
INIT_G();
if (argv[1]) {
if (argv[2])
bb_show_usage();
if (NOT_LONE_DASH(argv[1])) {
close(STDIN_FILENO); /* == 0 */
xopen(argv[1], O_RDONLY); /* fd will be 0 */
}
}
/* Read in words separated by <blank>s */
a = NULL;
line = NULL;
linesz = 0;
while ((len = getline(&line, &linesz, stdin)) != -1) {
char *s = line;
while (*(s = skip_whitespace(s)) != '\0') {
struct node *b;
char *word;
word = s;
s = skip_non_whitespace(s);
if (*s)
*s++ = '\0';
/* Create nodes and edges for each word pair */
b = get_node(word);
if (!a) {
a = b;
} else {
if (a != b)
add_edge(a, b);
a = NULL;
}
}
}
// Most other tools do not check for input read error (treat them as EOF)
// die_if_ferror(in, input_filename);
if (a)
bb_simple_error_msg_and_die("odd input");
free(line);
/*
* Kahn's algorithm:
* - find a node that has no incoming edges, print and remove it
* - repeat until the graph is empty
* - if any nodes are left, they form cycles.
*/
cycles = 0;
while (G.nodes_len) {
struct node *n;
unsigned i;
/* Search for first node with no incoming edges */
for (i = 0; i < G.nodes_len; i++) {
if (!G.nodes[i]->in_count)
break;
}
if (i == G.nodes_len) {
/* Must be a cycle; arbitraily break it at node 0 */
cycles++;
i = 0;
#ifndef TINY
bb_error_msg("cycle at %s", G.nodes[i]->name);
#endif
}
/* Remove the node (need no longer maintain sort) */
n = G.nodes[i];
G.nodes[i] = G.nodes[--G.nodes_len];
/* And remove its outgoing edges */
for (i = 0; i < n->out_count; i++)
n->out[i]->in_count--;
free(n->out);
puts(n->name);
free(n);
}
free(G.nodes);
fflush_stdout_and_exit(cycles ? 1 : 0);
}
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