Updated 1 solution

Author: RodneyShag

Chp. 04 - Trees and Graphs/_4_07_Build_Order/BuildOrder.java

@@ -1,15 +1,28 @@
 package _4_07_Build_Order;
 
-import java.util.List;
 import java.util.ArrayDeque;
 
 // From Jeff Erickson's Algorithms.pdf, Section 19.5 Topological Sort
 
 public class BuildOrder {
- public static ArrayDeque<Node> topologicalSort(List<Node> nodes) throws Exception {
- /* Create new "source" Node which has a directed edge to each node in our original graph */
- Node source = new Node('s');
- for (Node node : nodes) {
+
+ // Converts our inconveniently formatted input into a graph
+ public static ArrayDeque<Node> topologicalSort(String[] projects, String[][] dependencies) throws Exception {
+ Graph graph = new Graph();
+ for (String project : projects) {
+ graph.addNode(project);
+ }
+ for (String[] dependency : dependencies) {
+ String source = dependency[0];
+ String destination = dependency[1];
+ graph.addDirectedEdge(source, destination);
+ }
+ return topologicalSort(graph);
+ }
+
+ private static ArrayDeque<Node> topologicalSort(Graph graph) throws Exception {
+ Node source = new Node("Source");
+ for (Node node : graph.nodes) {
  source.addDirectedNeighbor(node);
  }
 
@@ -25,7 +38,7 @@ private static void topoSortDFS(Node n, ArrayDeque<Node> result) throws Exceptio
  if (neighbor.status == Visited.NEW) {
  topoSortDFS(neighbor, result);
  } else if (neighbor.status == Visited.ACTIVE) {
- throw new Exception("Not a DAG");
+ throw new Exception("Not a DAG. Graph has a cycle.");
  }
  }
  n.status = Visited.DONE;

Chp. 04 - Trees and Graphs/_4_07_Build_Order/Graph.java

@@ -0,0 +1,25 @@
+package _4_07_Build_Order;
+
+import java.util.*;
+
+public class Graph { // public variables for convenience
+ public List<Node> nodes;
+ public Map<String, Node> map;
+
+ public Graph() {
+ nodes = new ArrayList<>();
+ map = new HashMap<>();
+ }
+
+ public void addDirectedEdge(String s1, String s2) {
+ Node source = map.get(s1);
+ Node destination = map.get(s2);
+ source.addDirectedNeighbor(destination);
+ }
+
+ public void addNode(String str) {
+ Node node = new Node(str);
+ nodes.add(node);
+ map.put(str, node);
+ }
+}

Chp. 04 - Trees and Graphs/_4_07_Build_Order/Node.java

@@ -2,13 +2,12 @@
 
 import java.util.ArrayList;
 
-class Node {
- public char data;
+class Node { // public variables for convenience
+ public String data;
  public Visited status;
  public ArrayList<Node> neighbors; // could alternatively use a HashSet (if I give nodes unique IDs)
 
- /* Constructor */
- public Node(char data) {
+ public Node(String data) {
  this.data = data;
  status = Visited.NEW;
  neighbors = new ArrayList<>();

Chp. 04 - Trees and Graphs/_4_07_Build_Order/Tester.java

@@ -1,26 +1,20 @@
 package _4_07_Build_Order;
 
-import java.util.Arrays;
-import java.util.List;
-
 public class Tester {
  public static void main(String[] args) {
  System.out.println("*** Test 4.7: Build Order\n");
- Node a = new Node('a');
- Node b = new Node('b');
- Node c = new Node('c');
- Node d = new Node('d');
- Node e = new Node('e');
- Node f = new Node('f');
- a.addDirectedNeighbor(d);
- f.addDirectedNeighbor(b);
- b.addDirectedNeighbor(d);
- f.addDirectedNeighbor(a);
- d.addDirectedNeighbor(c);
- List<Node> nodes = Arrays.asList(a, b, c, d, e, f);
+ 
+ String[] projects = {"a", "b", "c", "d", "e", "f"};
+ String[][] dependencies = {
+ {"a", "d"},
+ {"f", "b"},
+ {"b", "d"},
+ {"f", "a"},
+ {"d", "c"}
+ };
 
  try {
- System.out.println(BuildOrder.topologicalSort(nodes));
+ System.out.println(BuildOrder.topologicalSort(projects, dependencies));
  } catch (Exception exc) {
  System.out.println(exc.getMessage());
  }

Chp. 16 - More Problems (Moderate)/_16_25_LRU_Cache/LRUCache.java

@@ -3,7 +3,7 @@
 import java.util.Map;
 import java.util.HashMap;
 
-// - Excellent explanation in Cracking the Coding Interview, 6th Edition solutions
+// Excellent explanation in Cracking the Coding Interview, 6th Edition solutions
 
 // FAQ
 //