Add Floyd-Warshall activity

Author: jcazevedo

src/main/java/com/packt/datastructuresandalg/lesson6/activity/floydwarshall/FloydWarshall.java

@@ -0,0 +1,35 @@
+package com.packt.datastructuresandalg.lesson6.activity.floydwarshall;
+
+import java.util.List;
+
+public class FloydWarshall {
+    int[][] adj;
+    int[][] path;
+
+    public FloydWarshall(int nodes) {
+        this.adj = new int[nodes][nodes];
+        this.path = new int[nodes][nodes];
+        for (int i = 0; i < adj.length; i++) {
+            for (int j = 0; j < adj[i].length; j++) {
+                if (i == j) {
+                    this.adj[i][j] = 0;
+                    this.path[i][j] = i;
+                } else {
+                    this.adj[i][j] = Integer.MAX_VALUE;
+                    this.path[i][j] = -1;
+                }
+            }
+        }
+    }
+
+    public void addEdge(int u, int v, int weight) {
+        if (weight < adj[u][v]) {
+            adj[u][v] = weight;
+            path[u][v] = u;
+        }
+    }
+
+    public List<Integer> path(int u, int v) { return null; }
+
+    public void run() { }
+}

src/main/java/com/packt/datastructuresandalg/lesson6/activity/floydwarshall/solution/FloydWarshall.java

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+package com.packt.datastructuresandalg.lesson6.activity.floydwarshall.solution;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FloydWarshall {
+    int[][] adj;
+    int[][] path;
+
+    public FloydWarshall(int nodes) {
+        this.adj = new int[nodes][nodes];
+        this.path = new int[nodes][nodes];
+        for (int i = 0; i < adj.length; i++) {
+            for (int j = 0; j < adj[i].length; j++) {
+                if (i == j) {
+                    this.adj[i][j] = 0;
+                    this.path[i][j] = i;
+                } else {
+                    this.adj[i][j] = Integer.MAX_VALUE;
+                    this.path[i][j] = -1;
+                }
+            }
+        }
+    }
+
+    public void addEdge(int u, int v, int weight) {
+        if (weight < adj[u][v]) {
+            adj[u][v] = weight;
+            path[u][v] = u;
+        }
+    }
+
+    public List<Integer> path(int u, int v) {
+        List<Integer> res = new ArrayList<>();
+        if (path[u][v] == -1)
+            return res;
+        int i = v;
+        while (u != i) {
+            res.add(0, i);
+            i = path[u][i];
+        }
+        res.add(0, u);
+        return res;
+    }
+
+    public void run() {
+        for (int k = 0; k < adj.length; k++) {
+            for (int i = 0; i < adj.length; i++) {
+                if (adj[i][k] >= Integer.MAX_VALUE)
+                    continue;
+                for (int j = 0; j < adj.length; j++) {
+                    if (adj[k][j] >= Integer.MAX_VALUE)
+                        continue;
+                    if (adj[i][k] + adj[k][j] < adj[i][j]) {
+                        adj[i][j] = adj[i][k] + adj[k][j];
+                        path[i][j] = path[k][j];
+                    }
+                }
+            }
+        }
+    }
+}

src/test/java/com/packt/datastructuresandalg/lesson6/activity/floydwarshall/FloydWarshallTest.java

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+package com.packt.datastructuresandalg.lesson6.activity.floydwarshall;
+
+import junit.framework.TestCase;
+
+import java.util.Arrays;
+
+public class FloydWarshallTest extends TestCase {
+    public void test() {
+        FloydWarshall f = new FloydWarshall(5);
+        f.addEdge(0, 1, 10);
+        f.addEdge(0, 3, 5);
+        f.addEdge(1, 3, 2);
+        f.addEdge(1, 2, 1);
+        f.addEdge(2, 4, 4);
+        f.addEdge(3, 1, 3);
+        f.addEdge(3, 2, 9);
+        f.addEdge(3, 4, 2);
+        f.addEdge(4, 2, 6);
+        f.run();
+
+        assertTrue(f.path(0, 0).equals(Arrays.asList(0)));
+        assertTrue(f.path(0, 1).equals(Arrays.asList(0, 3, 1)));
+        assertTrue(f.path(0, 2).equals(Arrays.asList(0, 3, 1, 2)));
+        assertTrue(f.path(0, 3).equals(Arrays.asList(0, 3)));
+        assertTrue(f.path(0, 4).equals(Arrays.asList(0, 3, 4)));
+        assertTrue(f.path(1, 4).equals(Arrays.asList(1, 3, 4)));
+    }
+}