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BuildOrder: done, time complexity: pending
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‎src/main/java/com/ctci/treesandgraphs/BuildOrder.java

+125-3
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,136 @@
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package com.ctci.treesandgraphs;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.LinkedHashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.Set;
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import java.util.stream.Stream;
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/**
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* @author rampatra
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* @since 2019-02-21
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*/
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public class BuildOrder {
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// todo
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private class Project {
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String name;
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Set<Project> dependencies = new HashSet<>();
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Project(String name) {
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this.name = name;
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}
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@Override
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public String toString() {
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return name;
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}
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}
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private final Map<String, Project> projects = new HashMap<>();
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private void addProjects(Stream<String> projectNames) {
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projectNames.forEach(name -> projects.put(name, new Project(name)));
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}
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/**
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* Adds a directed edge from {@code projectName2} to {@code ProjectName1}. This means {@code projectName2} is
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* dependent on {@code projectName1}, i.e, {@code projectName1} has to be built before {@code projectName2}.
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*
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* @param projectName1 name of project 1
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* @param projectName2 name of project 2
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*/
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private void addDependency(String projectName1, String projectName2) {
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Project p1 = projects.get(projectName1);
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Project p2 = projects.get(projectName2);
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if (p1 == null) {
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p1 = new Project(projectName1);
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projects.put(projectName1, p1);
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}
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if (p2 == null) {
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p2 = new Project(projectName2);
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projects.put(projectName2, p2);
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}
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p2.dependencies.add(p1);
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}
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/**
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* Determines the order in which the projects need to be built.
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* Time complexity: TODO
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*
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* @return a list of projects in the order they should be built, the first project should be built first and so on.
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*/
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private List<Project> getBuildOrder() {
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Map<String, Project> projectsBuilt = new LinkedHashMap<>(); // linked hashmap is needed to maintain the insertion order
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while (projectsBuilt.size() != projects.size()) {
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// find the projects which are not dependent on any project
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Set<Project> nextProjectsToBuild = getProjectsWithNoDependencies(projectsBuilt);
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// if there are no further independent projects to build, then we can't proceed further
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if (nextProjectsToBuild.size() == 0) {
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throw new IllegalStateException("Error: Projects can't be built.");
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}
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nextProjectsToBuild.forEach(p -> projectsBuilt.put(p.name, p));
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// once a project is built, remove the dependencies from all other projects dependent on this
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removeDependency(nextProjectsToBuild);
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}
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return new ArrayList<>(projectsBuilt.values());
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}
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private Set<Project> getProjectsWithNoDependencies(Map<String, Project> alreadyBuildProjects) {
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Set<Project> unBuiltProjectsWithZeroDependencies = new HashSet<>();
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for (Map.Entry<String, Project> entry : projects.entrySet()) {
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if (entry.getValue().dependencies.size() == 0 && alreadyBuildProjects.get(entry.getKey()) == null) {
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unBuiltProjectsWithZeroDependencies.add(entry.getValue());
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}
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}
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return unBuiltProjectsWithZeroDependencies;
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}
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private void removeDependency(Set<Project> newlyBuiltProjects) {
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projects.forEach((n, p) -> p.dependencies.removeAll(newlyBuiltProjects));
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}
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public static void main(String[] args) {
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/* test case 1
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––––––––––– b
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| ↑
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↓ |
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f <–– a <–– d <–– c
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*/
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BuildOrder buildOrder = new BuildOrder();
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buildOrder.addProjects(Stream.of("a", "b", "c", "d", "e", "f"));
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buildOrder.addDependency("a", "d");
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buildOrder.addDependency("f", "b");
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buildOrder.addDependency("b", "d");
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buildOrder.addDependency("f", "a");
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buildOrder.addDependency("d", "c");
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System.out.println(buildOrder.getBuildOrder());
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// test case 2
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buildOrder = new BuildOrder();
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buildOrder.addProjects(Stream.of("a", "b", "c", "d", "e", "f", "g"));
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buildOrder.addDependency("d", "g");
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buildOrder.addDependency("f", "b");
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buildOrder.addDependency("f", "c");
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buildOrder.addDependency("f", "a");
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buildOrder.addDependency("c", "a");
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buildOrder.addDependency("b", "a");
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buildOrder.addDependency("b", "e");
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buildOrder.addDependency("a", "e");
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System.out.println(buildOrder.getBuildOrder());
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}
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}
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}

‎src/main/java/com/ctci/treesandgraphs/RouteBetweenNodes.java

+64-64
Original file line numberDiff line numberDiff line change
@@ -13,82 +13,82 @@
1313
*/
1414
public class RouteBetweenNodes {
1515

16-
public static void main(String[] args) {
17-
Graph g = new Graph();
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g.addEdge(1, 2);
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g.addEdge(2, 3);
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g.addEdge(4, 5);
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g.addEdge(5, 6);
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System.out.println("Route exists from 1 to 2: " + g.isRoutePresent(1, 2));
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System.out.println("Route exists from 2 to 5: " + g.isRoutePresent(2, 5));
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System.out.println("Route exists from 1 to 3: " + g.isRoutePresent(1, 3));
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System.out.println("Route exists from 4 to 6: " + g.isRoutePresent(4, 6));
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System.out.println("Route exists from 6 to 4: " + g.isRoutePresent(6, 4));
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System.out.println("Route exists from 6 to 5: " + g.isRoutePresent(6, 5));
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}
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}
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class Graph {
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31-
class Graph {
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private final Map<Integer, GraphNode> nodes = new HashMap<>();
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33-
private static final Map<Integer, GraphNode> nodes = new HashMap<>();
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/**
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* Adds an edge from a node with value {@code v1} to another node with value {@code v2}.
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* Note: This code doesn't work for nodes having duplicate values.
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*
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* @param v1
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* @param v2
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*/
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void addEdge(int v1, int v2) {
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GraphNode n1 = nodes.get(v1);
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GraphNode n2 = nodes.get(v2);
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35-
/**
36-
* Adds an edge from a node with value {@code v1} to another node with value {@code v2}.
37-
* Note: This code doesn't work for nodes having duplicate values.
38-
*
39-
* @param v1
40-
* @param v2
41-
*/
42-
void addEdge(int v1, int v2) {
43-
GraphNode n1 = nodes.get(v1);
44-
GraphNode n2 = nodes.get(v2);
31+
if (n1 == null) {
32+
n1 = new GraphNode(v1);
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nodes.put(v1, n1);
34+
}
35+
if (n2 == null) {
36+
n2 = new GraphNode(v2);
37+
nodes.put(v2, n2);
38+
}
4539

46-
if (n1 == null) {
47-
n1 = new GraphNode(v1);
48-
nodes.put(v1, n1);
40+
n1.adjacent.add(n2); // as it is a directed graph
4941
}
50-
if (n2 == null) {
51-
n2 = new GraphNode(v2);
52-
nodes.put(v2, n2);
53-
}
54-
55-
n1.adjacent.add(n2); // as it is a directed graph
56-
}
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58-
/**
59-
* Checks for a path from a node with value {@code v1} to another node with value {@code v2} in a breadth-first
60-
* manner. Note: This code doesn't work for nodes having duplicate values.
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*
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* @param v1 the value of the first node or starting node.
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* @param v2 the value of the ending node.
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* @return {@code true} if path exists, {@code false} otherwise.
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*/
66-
boolean isRoutePresent(int v1, int v2) {
67-
Queue<GraphNode> queue = new ArrayDeque<>();
68-
Set<GraphNode> visited = new HashSet<>();
43+
/**
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* Checks for a path from a node with value {@code v1} to another node with value {@code v2} in a breadth-first
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* manner. Note: This code doesn't work for nodes having duplicate values.
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*
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* @param v1 the value of the first node or starting node.
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* @param v2 the value of the ending node.
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* @return {@code true} if path exists, {@code false} otherwise.
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*/
51+
boolean isRoutePresent(int v1, int v2) {
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Queue<GraphNode> queue = new ArrayDeque<>();
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Set<GraphNode> visited = new HashSet<>();
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70-
GraphNode n1 = nodes.get(v1);
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GraphNode n2 = nodes.get(v2);
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GraphNode n1 = nodes.get(v1);
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GraphNode n2 = nodes.get(v2);
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73-
if (n1 == null || n2 == null) {
74-
return false;
75-
}
58+
if (n1 == null || n2 == null) {
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return false;
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}
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77-
queue.add(n1);
62+
queue.add(n1);
7863

79-
while (!queue.isEmpty()) {
80-
GraphNode n = queue.poll();
64+
while (!queue.isEmpty()) {
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GraphNode n = queue.poll();
8166

82-
if (visited.contains(n)) {
83-
continue;
84-
}
85-
if (n.adjacent.contains(n2)) {
86-
return true;
67+
if (visited.contains(n)) {
68+
continue;
69+
}
70+
if (n.adjacent.contains(n2)) {
71+
return true;
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}
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queue.addAll(n.adjacent);
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visited.add(n);
8775
}
88-
queue.addAll(n.adjacent);
89-
visited.add(n);
76+
77+
return false;
9078
}
79+
}
9180

92-
return false;
81+
public static void main(String[] args) {
82+
Graph g = new RouteBetweenNodes().new Graph();
83+
g.addEdge(1, 2);
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g.addEdge(2, 3);
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g.addEdge(4, 5);
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g.addEdge(5, 6);
87+
System.out.println("Route exists from 1 to 2: " + g.isRoutePresent(1, 2));
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System.out.println("Route exists from 2 to 5: " + g.isRoutePresent(2, 5));
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System.out.println("Route exists from 1 to 3: " + g.isRoutePresent(1, 3));
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System.out.println("Route exists from 4 to 6: " + g.isRoutePresent(4, 6));
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System.out.println("Route exists from 6 to 4: " + g.isRoutePresent(6, 4));
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System.out.println("Route exists from 6 to 5: " + g.isRoutePresent(6, 5));
9393
}
94-
}
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}

‎src/main/java/com/rampatra/database/README.md

+22
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@@ -1,5 +1,27 @@
11
# Relational Database (WIP)
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3+
A __relational database__ is a digital database based on
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the [relational model](https://en.wikipedia.org/wiki/Relational_model) of
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data. In simple words, it is a collection of data items with pre-defined
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relationships between them. These items are organized as a set of tables,
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with columns and rows. Each column stores some specific attribute of an object/entity and the
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row represents a specific object/entity.
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A software system used to maintain relational databases is a __relational
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database management system (RDBMS)__, for e.g., MySQL, Oracle DB, PostgreSQL, etc.
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Virtually all relational database systems use __SQL (Structured Query Language)__
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for querying and maintaining the database.
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## Basic Definitions
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1. Primary Key
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2. Candidate Key
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3. Composite Key
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4. Prime/Non-prime attribute
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## Types of SQL commands
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527
1. DDL

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