08-27-周三_17-09-29

node_modules/graphlibrary/lib/alg/prim.js

@@ -0,0 +1,52 @@
+const _ = require('../lodash')
+const Graph = require('../graph')
+const PriorityQueue = require('../data/priority-queue')
+
+module.exports = prim
+
+function prim (g, weightFunc) {
+  const result = new Graph()
+  const parents = {}
+  const pq = new PriorityQueue()
+  let v
+
+  function updateNeighbors (edge) {
+    const w = edge.v === v ? edge.w : edge.v
+    const 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
+}