Finding the cycle in an undirected graph using BFS - graph

Question

I want to find first cycle in an undirected graph using BFS only(NOT DFS). All sources solved this problem with DFS but I have to find it using BFS. How can I find it? Thanks in advance!

Answer 1

Here below you will find the code to traverse a graph using BFS and find its cycles.
#include <stdio.h>
#include <queue>
using namespace std;
int nodes, edges, src;
int graph[100][100], color[100], prev[100];
const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
void print(int);
int main() {
printf("Nodes, edges, source? ");
scanf("%d %d %d ", &nodes, &edges, &src);
for(int i = 1; i <= edges; i++) {
printf("Edge %d: ", i);
int x, y;
scanf("%d %d", &x, &y);
graph[x][y] = 1;
}
//run BFS
queue<int> q; //create a queue
q.push(src); //1. put root node on the queue
do{
int u = q.front(); //2. pull a node from the beginning of the queue
q.pop();
printf("%d ", u); //print the node
for(int i = 1; i <= nodes; i++) { //4. get all the adjacent nodes
if((graph[u][i] == 1) //if an edge exists between these two nodes,
&& (color[i] == WHITE)) { //and this adjacent node is still WHITE,
q.push(i); //4. push this node into the queue
color[i] = GRAY; //color this adjacent node with GRAY
}
}
color[u] = BLACK; //color the current node black to mark it as dequeued
} while(!q.empty()); //5. if the queue is empty, then all the nodes havebeen visited
//find and print cycle from source
for(int i = 1; i <= nodes; i++) {
if(graph[i][src] == 1) {
print(i);
printf("%d\n\n", src);
}
}
return 0;
}
void print(int node) {
if(node == 0)
return;
print(prev[node]);
printf("%d -> ", node);
}
Also I recommend you to take a look at this brief and useful guide.