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detect cycle in DIRECTED graph.cpp
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detect cycle in DIRECTED graph.cpp
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/*
///////////////////////////////////////////
//Question/Info
Detect cycle in a directed graph
Medium Accuracy: 30.19% Submissions: 97622 Points: 4
Given a Directed Graph with V vertices (Numbered from 0 to V-1) and E edges, check whether it contains any cycle or not.
IT HAS DFS APPROACH
AND BFS APPROACH (KAHN'S ALGO.)
Example 1:
Input:
Output: 1
Explanation: 3 -> 3 is a cycle
Example 2:
Input:
Output: 0
Explanation: no cycle in the graph
Your task:
You donβt need to read input or print anything. Your task is to complete the function isCyclic() which takes the integer V denoting the number of vertices and adjacency list as input parameters and returns a boolean value denoting if the given directed graph contains a cycle or not.
Expected Time Complexity: O(V + E)
Expected Auxiliary Space: O(V)
Constraints:
1 β€ V, E β€ 105
Company Tags
Adobe Amazon BankBazaar Flipkart Goldman Sachs MakeMyTrip Microsoft Oracle Rockstand Samsung
author: srj_v
///////////////////////////////////////////
*/
#include <bits/stdc++.h>
using namespace std;
#define _IOS ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
typedef long double ld;
typedef long long int lli;
#pragma GCC optimize("Ofast")
void c_p_c()
{
#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
}
int32_t main() {
///////////
c_p_c();
///////////
_IOS
//////////
// code
/*
int t ; cin >> t; while(t--){}
*/
class Solution
{
public:
bool dcycleDFS(vector<int> adj[], vector<int> &vis, vector<int> &dfsa, int node) {
vis[node] = 1;
dfsa[node] = 1;
for (auto x : adj[node]) {
if (!vis[x]) {
if (dcycleDFS(adj, vis, dfsa, x)) {
return true;
}
}
else if (vis[x] and dfsa[x]) {
// we check both visited array and the dfs array...
// both should be true if there's a cycle in directed graph ...
return true;
}
}
// marking it back to zero if we reach the end....
// the original visited array wouldn't be altered, but this would be...
dfsa[node] = 0;
return false;
}
/*
TO USE BFS ALGO TO DETECT THE CYCLE, WE USE THE REVERSE LOGIC
OF TOPOLOGICAL SORT ~ KAHN'S ALGORITHM. SINCE TOPOLOGICAL SORT EXISTS ONLY
IN A DIRECTED ACYCLIC GRAPH, IF WE ARE UNABLE TO GENERATE A
TOPOLOGICAL SORT THEN ITS A CYCLIC GRAPH...!
*/
//Function to detect cycle in a directed graph.
bool isCyclic(int V, vector<int> adj[])
{
// code here
vector<int> vis(V + 1);
vector<int>dfsa(V + 1);
for (int i = 0 ; i < V ; i++) {
if (!vis[i]) {
if (dcycleDFS(adj, vis, dfsa, i)) {
return true;
}
}
}
return false;
}
};
// cerr << "time: " << clock() << " ms" << '\n';
return 0;
}