reorg and add code for second edition

09_dijkstras_algorithm/javascript/01_dijkstras_algorithm.js

@@ -0,0 +1,79 @@
+"use strict";
+
+// the graph
+const graph = {};
+graph["start"] = {};
+graph["start"]["a"] = 6;
+graph["start"]["b"] = 2;
+
+graph["a"] = {};
+graph["a"]["fin"] = 1;
+
+graph["b"] = {};
+graph["b"]["a"] = 3;
+graph["b"]["fin"] = 5;
+
+graph["fin"] = {};
+
+// The costs table
+const costs = {};
+costs["a"] = 6;
+costs["b"] = 2;
+costs["fin"] = Infinity;
+
+// the parents table
+const parents = {};
+parents["a"] = "start";
+parents["b"] = "start";
+parents["fin"] = null;
+
+let processed = [];
+
+/**
+ * Find the lowest node
+ * @param {Object} itCosts Hash table
+ * @returns {(string|null)} The lowest node
+ */
+function findLowestCostNode(costs) {
+  let lowestCost = Infinity;
+  let lowestCostNode = null;
+
+  // Go through each node
+  for (let node in costs) {
+    const cost = costs[node];
+    // If it's the lowest cost so far and hasn't been processed yet...
+    if (cost < lowestCost && processed.indexOf(node) === -1) {
+      // ... set it as the new lowest-cost node.
+      lowestCost = cost;
+      lowestCostNode = node;
+    }
+  }
+  return lowestCostNode;
+}
+
+let node = findLowestCostNode(costs);
+
+while (node !== null) {
+  const cost = costs[node];
+  // Go through all the neighbors of this node
+  const neighbors = graph[node];
+  Object.keys(neighbors).forEach(function(n) {
+    const new_cost = cost + neighbors[n];
+    // If it's cheaper to get to this neighbor by going through this node
+    if (costs[n] > new_cost) {
+      // ... update the cost for this node
+      costs[n] = new_cost;
+      // This node becomes the new parent for this neighbor.
+      parents[n] = node;
+    }
+  });
+
+  // Mark the node as processed
+  processed = processed.concat(node);
+
+  // Find the next node to process, and loop
+  node = findLowestCostNode(costs);
+}
+
+console.log("Cost from the start to each node:");
+console.log(costs); // { a: 5, b: 2, fin: 6 }