code for chapter 7 in javascript

07_dijkstras_algorithm/javascript/01_dijkstras_algorithm.js

@@ -0,0 +1,75 @@
+'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 = [];
+
+
+function find_lowest_cost_node(costs) {
+  let lowest_cost = Infinity;
+  let lowest_cost_node = null;
+
+  // Go through each node
+  for (let node in costs) {
+    let cost = costs[node];
+    // If it's the lowest cost so far and hasn't been processed yet...
+    if (cost < lowest_cost && (processed.indexOf(node) === -1)) {
+      // ... set it as the new lowest-cost node.
+      lowest_cost = cost;
+      lowest_cost_node = node;
+    }
+  }
+  return lowest_cost_node;
+}
+
+let node = find_lowest_cost_node(costs);
+
+while (node !== null) {
+  let cost = costs[node];
+  // Go through all the neighbors of this node
+  let neighbors = graph[node];
+  Object.keys(neighbors).forEach(function(n) {
+    let 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 = find_lowest_cost_node(costs);
+}
+
+console.log("Cost from the start to each node:");
+console.log(costs); // { a: 5, b: 2, fin: 6 }