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2360. Longest Cycle in a Graph

Description

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

Solutions

• Java
• C++
• Python
• Go
• TypeScript

• class Solution {
      public int longestCycle(int[] edges) {
          int n = edges.length;
          boolean[] vis = new boolean[n];
          int ans = -1;
          for (int i = 0; i < n; ++i) {
              if (vis[i]) {
                  continue;
              }
              int j = i;
              List<Integer> cycle = new ArrayList<>();
              for (; j != -1 && !vis[j]; j = edges[j]) {
                  vis[j] = true;
                  cycle.add(j);
              }
              if (j == -1) {
                  continue;
              }
              for (int k = 0; k < cycle.size(); ++k) {
                  if (cycle.get(k) == j) {
                      ans = Math.max(ans, cycle.size() - k);
                      break;
                  }
              }
          }
          return ans;
      }
  }
  

• class Solution {
  public:
      int longestCycle(vector<int>& edges) {
          int n = edges.size();
          vector<bool> vis(n);
          int ans = -1;
          for (int i = 0; i < n; ++i) {
              if (vis[i]) {
                  continue;
              }
              int j = i;
              vector<int> cycle;
              for (; j != -1 && !vis[j]; j = edges[j]) {
                  vis[j] = true;
                  cycle.push_back(j);
              }
              if (j == -1) {
                  continue;
              }
              for (int k = 0; k < cycle.size(); ++k) {
                  if (cycle[k] == j) {
                      ans = max(ans, (int) cycle.size() - k);
                      break;
                  }
              }
          }
          return ans;
      }
  };
  

• 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
  
  

• func longestCycle(edges []int) int {
  	vis := make([]bool, len(edges))
  	ans := -1
  	for i := range edges {
  		if vis[i] {
  			continue
  		}
  		j := i
  		cycle := []int{}
  		for ; j != -1 && !vis[j]; j = edges[j] {
  			vis[j] = true
  			cycle = append(cycle, j)
  		}
  		if j == -1 {
  			continue
  		}
  		for k := range cycle {
  			if cycle[k] == j {
  				ans = max(ans, len(cycle)-k)
  				break
  			}
  		}
  	}
  	return ans
  }
  

• function longestCycle(edges: number[]): number {
      const n = edges.length;
      const vis = new Array(n).fill(false);
      let ans = -1;
      for (let i = 0; i < n; ++i) {
          if (vis[i]) {
              continue;
          }
          let j = i;
          const cycle: number[] = [];
          for (; j != -1 && !vis[j]; j = edges[j]) {
              vis[j] = true;
              cycle.push(j);
          }
          if (j == -1) {
              continue;
          }
          for (let k = 0; k < cycle.length; ++k) {
              if (cycle[k] == j) {
                  ans = Math.max(ans, cycle.length - k);
                  break;
              }
          }
      }
      return ans;
  }
  
  

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