Longest Cycle in a Graph — LeetCode 2360 Python Solution

The problem

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].

Example

Input

edges = [3,3,4,2,3]

Output

3

Explanation

The longest cycle in the graph is the cycle: 2 -> 4 -> 3 -> 2.

Python solution

class Solution:
    def longestCycle(self, edges: List[int]) -> int:
        n = len(edges)
        vis = [False] * n
        ans = -1
        for i in range(n):
            if vis[i]:
                continue
            j = i
            cycle = []
            while j != -1 and not vis[j]:
                vis[j] = True
                cycle.append(j)
                j = edges[j]
            if j == -1:
                continue
            m = len(cycle)
            k = next((k for k in range(m) if cycle[k] == j), inf)
            ans = max(ans, m - k)
        return ans

Complexity

Pattern: Topological Sort

Order a set of tasks so that every dependency comes before the thing that needs it. LeetCode 2360. Longest Cycle in a Graph is filed here because LeetCode tags it Topological Sort, which is the vocabulary this hub collects.

The topological sort guide has the Python template for the pattern and the 32 LeetCode problems that use it.

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