main.js

// URL: https://leetcode.com/problems/longest-cycle-in-a-graph/

/**
 * @param {number[]} edges
 * @return {number}
 */
var longestCycle = function (edges) {
  // visited array will be -1 if not visited or index of first visited node
  const visited = Array(edges.length).fill(-1);
  let ans = -1;

  for (let i = 0; i < edges.length; i++) {
    // Since one node could be part of only one solution, only compute if it is not already visited.
    if (visited[i] !== -1) continue;

    // detect cycle: check if node is already visited
    // if it was visited and the visited[i] === i,
    // it means we came to this node during this iteration
    // hence find the length

    let currNode = i;

    while (currNode !== -1) {
      // if not already visited, mark as visited
      if (visited[currNode] === -1) {
        visited[currNode] = i;
        currNode = edges[currNode];
        continue;
      }

      // if already visited, and value is equal to current index
      // it means we came to node during this iteration, hence we found the cycle
      if (visited[currNode] === i) {
        // find the cycle length
        let currCycleLen = 1;
        let cycleStartNode = currNode;
        currNode = edges[currNode];

        // revisit all the nodes since first cycle node and note the length
        while (currNode !== cycleStartNode) {
          currCycleLen++;
          currNode = edges[currNode];
        }
        ans = Math.max(currCycleLen, ans);
      }
      break;
    }
  }
  // console.log(visited)
  return ans;
};