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.
Test Cases
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.
Solution
class Solution {
public int longestCycle(int[] edges) {
int longestCycleLen = -1;
int timeStep = 1;
int[] nodeVisitedAtTime = new int[edges.length];
for (int currentNode = 0; currentNode < edges.length; ++currentNode) {
if (nodeVisitedAtTime[currentNode] > 0)
continue;
final int startTime = timeStep;
int u = currentNode;
while (u != -1 && nodeVisitedAtTime[u] == 0) {
nodeVisitedAtTime[u] = timeStep++;
u = edges[u];
}
if (u != -1 && nodeVisitedAtTime[u] >= startTime)
longestCycleLen = Math.max(longestCycleLen, timeStep - nodeVisitedAtTime[u]);
}
return longestCycleLen;
}
}