53 lines
1.1 KiB
JavaScript
53 lines
1.1 KiB
JavaScript
var _ = require("../lodash");
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var Graph = require("../graph");
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var PriorityQueue = require("../data/priority-queue");
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module.exports = prim;
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function prim(g, weightFunc) {
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var result = new Graph();
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var parents = {};
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var pq = new PriorityQueue();
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var v;
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function updateNeighbors(edge) {
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var w = edge.v === v ? edge.w : edge.v;
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var pri = pq.priority(w);
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if (pri !== undefined) {
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var edgeWeight = weightFunc(edge);
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if (edgeWeight < pri) {
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parents[w] = v;
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pq.decrease(w, edgeWeight);
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}
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}
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}
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if (g.nodeCount() === 0) {
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return result;
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}
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_.each(g.nodes(), function(v) {
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pq.add(v, Number.POSITIVE_INFINITY);
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result.setNode(v);
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});
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// Start from an arbitrary node
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pq.decrease(g.nodes()[0], 0);
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var init = false;
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while (pq.size() > 0) {
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v = pq.removeMin();
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if (_.has(parents, v)) {
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result.setEdge(v, parents[v]);
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} else if (init) {
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throw new Error("Input graph is not connected: " + g);
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} else {
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init = true;
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}
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g.nodeEdges(v).forEach(updateNeighbors);
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}
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return result;
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}
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