dagre-d3-es/src/graphlib/alg/find-cycles.js

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import * as _ from 'lodash-es';
import { tarjan } from './tarjan.js';

/**
 * @import { Graph, NodeID } from '../graph.js';
 */

export { findCycles };

/**
 * Given a Graph, `g`, this function returns all nodes that
 * are part of a cycle. As there may be more than one cycle in a graph this
 * function return an array of these cycles, where each cycle is itself
 * represented by an array of ids for each node involved in that cycle.
 *
 * @remarks
 *
 * {@link isAcyclic} is more efficient if you only need to
 * determine whether a graph has a cycle or not.
 *
 * @example
 *
 * ```js
 * var g = new graphlib.Graph();
 * g.setNode(1);
 * g.setNode(2);
 * g.setNode(3);
 * g.setEdge(1, 2);
 * g.setEdge(2, 3);
 *
 * graphlib.alg.findCycles(g);
 * // => []
 *
 * g.setEdge(3, 1);
 * graphlib.alg.findCycles(g);
 * // => [ [ '3', '2', '1' ] ]
 *
 * g.setNode(4);
 * g.setNode(5);
 * g.setEdge(4, 5);
 * g.setEdge(5, 4);
 * graphlib.alg.findCycles(g);
 * // => [ [ '3', '2', '1' ], [ '5', '4' ] ]
 * ```
 *
 * @param {Graph} g - The graph to analyze.
 * @returns {NodeID[][]} An array of cycles. Each cycle is itself an array
 * that contains the ids of all nodes in the cycle.
 */
function findCycles(g) {
  return _.filter(tarjan(g), function (cmpt) {
    return cmpt.length > 1 || (cmpt.length === 1 && g.hasEdge(cmpt[0], cmpt[0]));
  });
}