এই প্রোগ্রামে আমরা মূলত একটি ফিডব্যাক আর্ক সেট (feedback arc set) বের করব যাতে এজগুলো যদি গ্রাফ থেকে রিমুভ করা হয়, তবে গ্রাফটি ডিরেক্টেড অ্যাসাইক্লিক গ্রাফ (DAG) হয়ে যায়।
আলগরিদম
Begin function checkCG(int n) : n: количество вершин. arr: struct graph переменная.
Initialize cnt = 0 and size = (n-1).
For i = 0 to n-1
if (cnt == size) return 0
if (arr[i].ptr == NULL)
Increase cnt.
for j = 0 to n-1
while (arr[j].ptr != NULL)
if ((arr[j].ptr)->des == (arr[i].ptr)->des)
(arr[j].ptr)->des = -1
arr[i].ptr = (arr[i].ptr)->next
Done
Done
Done
Done
initialize visited[n + 1]
For i = 0 to n-1
while (arr[i].ptr != NULL)
Print (arr[i].ptr)->des
visited[i] = 1
for j = 0 to n-1
while (arr[j].ptr != NULL)
print (arr[j].ptr)->des
if (visited[arr[j].v] == 1)
print arr[i].v << " - " << arr[j].v
Done
Done
arr[i].ptr = (arr[i].ptr)->next
Done
Done
return 1
End
উদাহরণ
#include <iostream>
using namespace std;
int c = 0;
struct ad_list {
int des;
ad_list *next;
} *np = NULL, *np1 = NULL, *p = NULL, *q = NULL;
struct Graph {
int v;
ad_list *ptr;
} arr[6];
void addRevEdge(int sr, int des) {
np1 = new ad_list;
np1->des = sr;
np1->next = NULL;
if (arr[des].ptr == NULL) {
arr[des].ptr = np1;
q = arr[des].ptr;
q->next = NULL;
} else {
q = arr[des].ptr;
while (q->next != NULL) q = q->next;
q->next = np1;
}
}
void addEd(int sr, int des) {
np = new ad_list;
np->des = des;
np->next = NULL;
if (arr[sr].ptr == NULL) {
arr[sr].ptr = np;
p = arr[sr].ptr;
p->next = NULL;
} else {
p = arr[sr].ptr;
while (p->next != NULL) p = p->next;
p->next = np;
}
}
void print_graph(int n) {
for (int i = 0; i < n; i++) {
cout << "Adjacency List of " << arr[i].v << ": ";
while (arr[i].ptr != NULL) {
cout << (arr[i].ptr)->des << " ";
arr[i].ptr = (arr[i].ptr)->next;
}
cout << endl;
}
}
int checkCG(int n) {
int cnt = 0;
int size = n - 1;
for (int i = 0; i < n; i++) {
if (cnt == size) return 0;
if (arr[i].ptr == NULL) {
cnt++;
for (int j = 0; j < n; j++) {
while (arr[j].ptr != NULL) {
if ((arr[j].ptr)->des == (arr[i].ptr)->des) {
(arr[j].ptr)->des = -1;
}
arr[i].ptr = (arr[i].ptr)->next;
}
}
}
}
cout << "after checking dag";
int visited[n + 1];
for (int i = 0; i < n; i++) {
while (arr[i].ptr != NULL) {
cout << (arr[i].ptr)->des << " ";
visited[i] = 1;
for (int j = 0; j < n; j++) {
while (arr[j].ptr != NULL) {
cout << (arr[j].ptr)->des << " ";
if (visited[arr[j].v] == 1) {
cout << arr[i].v << " - " << arr[j].v;
}
arr[j].ptr = (arr[j].ptr)->next;
}
cout << endl;
}
arr[i].ptr = (arr[i].ptr)->next;
}
cout << endl;
}
return 1;
}
int main() {
int n = 5;
cout << "Number of vertices: " << n << endl;
for (int i = 0; i < n; i++) {
arr[i].v = i;
arr[i].ptr = NULL;
}
addEd(1, 2);
addEd(2, 1);
addEd(0, 1);
addEd(2, 3);
addEd(2, 0);
addEd(5, 4);
addEd(4, 2);
print_graph(n);
cout << "Feedback arc Set: ";
if (checkCG(n) == 0)
cout << " None";
}
আউটপুট
Number of vertices: 5 Adjacency List of 0: 1 Adjacency List of 1: 2 Adjacency List of 2: 1 3 0 Adjacency List of 3: Adjacency List of 4: 2 Feedback arc Set: None
