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# Longest Cycle in a Graph LeetCode Solution

## Problem – Longest Cycle in a Graph LeetCode Solution

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`

### Longest Cycle in a Graph LeetCode Solution in C++

``````   int maxLength = -1;

void getcycle(vector<int> &edges,int si,vector<bool>& visit,int size,vector<int>& store){
if(si == -1)return ;
if(visit[si]){
int count = -1;
for(int i =0;i<store.size();i++){
if(store[i]==si){
count = i;
break;
} }

if(count==-1)return;
maxLength = max(maxLength,size-count);  // size-count gives the proper size of cycle
return ;
}

visit[si] = true;
store.push_back(si);
getcycle(edges,edges[si],visit,size+1,store);

return ;

}

int longestCycle(vector<int>& edges) {

vector<bool> visit(edges.size(),0);
for(int i =0;i<edges.size();i++){

if(visit[i])continue;
vector<int> store;
getcycle(edges,i,visit,0,store);

}

return maxLength;

}
``````

### Longest Cycle in a Graph LeetCode Solution in Java

``````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;
int dist = 0, idx = i;
HashMap<Integer, Integer> x = new HashMap<>();  // local visited
while(idx!=-1){
if(x.containsKey(idx)){
res = Math.max(res, dist-x.get(idx));
break;
}
if(vis[idx]) break;
vis[idx] = true;
x.put(idx, dist++);
idx = edges[idx];
}
}
return res;
}
``````

### Longest Cycle in a Graph LeetCode Solution in Python

``````def longestCycle(self, edges: List[int]) -> int:
n = len(edges)
self.max_length = float('-inf')
seen = [False] * n
visiting = {}
stack = []

def dfs(node):
if not seen[node]:
if node in visiting:
self.max_length = max(self.max_length, len(stack) - visiting[node])
elif edges[node] != -1:
visiting[node] = len(stack)
stack.append(node)
dfs(edges[node])
stack.pop()
visiting.pop(node)
seen[node] = True

for i in range(n):
dfs(i)
return self.max_length if self.max_length > 0 else -1    ``````
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