Leetcode 2360 Longest Cycle in a Graph Solution in Java | Hindi Coding Community

 

You are given a directed graph of n nodes numbered from 0 to n - 1, where each node has at most one outgoing edge.

The graph is represented with a given 0-indexed array edges of size n, indicating that there is a directed edge from node i to node edges[i]. If there is no outgoing edge from node i, then edges[i] == -1.

Return the length of the longest cycle in the graph. If no cycle exists, return -1.

A cycle is a path that starts and ends at the same node.

 

Example 1:

Input: edges = [3,3,4,2,3]
Output: 3
Explanation: The longest cycle in the graph is the cycle: 2 -> 4 -> 3 -> 2.
The length of this cycle is 3, so 3 is returned.

Example 2:

Input: edges = [2,-1,3,1]
Output: -1
Explanation: There are no cycles in this graph.

 

Constraints:

• n == edges.length
• 2 <= n <= 105
• -1 <= edges[i] < n
• edges[i] != i

Java Code :

public int longestCycle(int[] edges) {

int res = -1;

boolean[] vis = new boolean[edges.length]; // global visisted

for(int i=0; i<edges.length; i++){

if(vis[i]) continue;

HashMap<Integer, Integer> x = new HashMap<>(); // local visited

for (int idx=i, dist=0; idx!=-1; idx=edges[idx]){

if(x.containsKey(idx)){

res = Math.max(res, dist-x.get(idx));

break;

}

if(vis[idx]) break;

vis[idx] = true;

x.put(idx, dist++);

}

}

return res;

}