08-27-周三_17-09-29

node_modules/graphlib/lib/alg/prim.js

@@ -0,0 +1,52 @@
+var _ = require("../lodash");
+var Graph = require("../graph");
+var PriorityQueue = require("../data/priority-queue");
+
+module.exports = prim;
+
+function prim(g, weightFunc) {
+  var result = new Graph();
+  var parents = {};
+  var pq = new PriorityQueue();
+  var v;
+
+  function updateNeighbors(edge) {
+    var w = edge.v === v ? edge.w : edge.v;
+    var pri = pq.priority(w);
+    if (pri !== undefined) {
+      var edgeWeight = weightFunc(edge);
+      if (edgeWeight < pri) {
+        parents[w] = v;
+        pq.decrease(w, edgeWeight);
+      }
+    }
+  }
+
+  if (g.nodeCount() === 0) {
+    return result;
+  }
+
+  _.each(g.nodes(), function(v) {
+    pq.add(v, Number.POSITIVE_INFINITY);
+    result.setNode(v);
+  });
+
+  // Start from an arbitrary node
+  pq.decrease(g.nodes()[0], 0);
+
+  var init = false;
+  while (pq.size() > 0) {
+    v = pq.removeMin();
+    if (_.has(parents, v)) {
+      result.setEdge(v, parents[v]);
+    } else if (init) {
+      throw new Error("Input graph is not connected: " + g);
+    } else {
+      init = true;
+    }
+
+    g.nodeEdges(v).forEach(updateNeighbors);
+  }
+
+  return result;
+}