Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 26

Description

Longest Cycle in a Graph

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

Solution

class Solution {
public:
  int longestCycle(vector<int>& edges) {
    int n = edges.size();
    if(n < 2) return -1;
    vector<int> degree(n);
    set<int> visit;

    int answer = -1;
    for(int i = 0; i < n; ++i) {
      if(degree[i]) continue;
      int current = i;
      int prev;
      int d = 1;
      visit.clear();
      while(current != -1) {
        if(degree[current] && !visit.count(current)) break;
        if(visit.count(current)) {
          answer = max(answer, degree[prev] - degree[current] + 1);
          break;
        }
        degree[current] = d;
        d += 1;
        visit.insert(current);
        prev = current;
        current = edges[current];
      }
    }

    return answer;
  }
};

// Accepted
// 76/76 cases passed (554 ms)
// Your runtime beats 32.08 % of cpp submissions
// Your memory usage beats 43.72 % of cpp submissions (153.5 MB)