dist-javascript-algorithms-and-data-structures/dist/algorithms/graph/detect-cycle/detectUndirectedCycle.js

Algorithms and data-structures implemented on JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = detectUndirectedCycle;

var _depthFirstSearch = _interopRequireDefault(require("../depth-first-search/depthFirstSearch"));

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

/**
 * Detect cycle in undirected graph using Depth First Search.
 *
 * @param {Graph} graph
 */
function detectUndirectedCycle(graph) {
  let cycle = null; // List of vertices that we have visited.

  const visitedVertices = {}; // List of parents vertices for every visited vertex.

  const parents = {}; // Callbacks for DFS traversing.

  const callbacks = {
    allowTraversal: ({
      currentVertex,
      nextVertex
    }) => {
      // Don't allow further traversal in case if cycle has been detected.
      if (cycle) {
        return false;
      } // Don't allow traversal from child back to its parent.


      const currentVertexParent = parents[currentVertex.getKey()];
      const currentVertexParentKey = currentVertexParent ? currentVertexParent.getKey() : null;
      return currentVertexParentKey !== nextVertex.getKey();
    },
    enterVertex: ({
      currentVertex,
      previousVertex
    }) => {
      if (visitedVertices[currentVertex.getKey()]) {
        // Compile cycle path based on parents of previous vertices.
        cycle = {};
        let currentCycleVertex = currentVertex;
        let previousCycleVertex = previousVertex;

        while (previousCycleVertex.getKey() !== currentVertex.getKey()) {
          cycle[currentCycleVertex.getKey()] = previousCycleVertex;
          currentCycleVertex = previousCycleVertex;
          previousCycleVertex = parents[previousCycleVertex.getKey()];
        }

        cycle[currentCycleVertex.getKey()] = previousCycleVertex;
      } else {
        // Add next vertex to visited set.
        visitedVertices[currentVertex.getKey()] = currentVertex;
        parents[currentVertex.getKey()] = previousVertex;
      }
    }
  }; // Start DFS traversing.

  const startVertex = graph.getAllVertices()[0];
  (0, _depthFirstSearch.default)(graph, startVertex, callbacks);
  return cycle;
}