refactor: FordFulkerson (#5384)

Author: alxkm

src/main/java/com/thealgorithms/dynamicprogramming/FordFulkerson.java

@@ -2,76 +2,54 @@
 
 import java.util.LinkedList;
 import java.util.Queue;
-import java.util.Vector;
 
 public final class FordFulkerson {
-    private FordFulkerson() {
-    }
-
-    static final int INF = 987654321;
-    // edges
-    static int vertexCount;
-    static int[][] capacity;
-    static int[][] flow;
+    private static final int INF = Integer.MAX_VALUE;
 
-    public static void main(String[] args) {
-        System.out.println("Vertex Count : 6");
-        vertexCount = 6;
-        capacity = new int[vertexCount][vertexCount];
-
-        capacity[0][1] = 12;
-        capacity[0][3] = 13;
-        capacity[1][2] = 10;
-        capacity[2][3] = 13;
-        capacity[2][4] = 3;
-        capacity[2][5] = 15;
-        capacity[3][2] = 7;
-        capacity[3][4] = 15;
-        capacity[4][5] = 17;
-
-        System.out.println("Max capacity in networkFlow : " + networkFlow(0, 5));
+    private FordFulkerson() {
     }
 
-    private static int networkFlow(int source, int sink) {
-        flow = new int[vertexCount][vertexCount];
+    public static int networkFlow(int vertexCount, int[][] capacity, int[][] flow, int source, int sink) {
         int totalFlow = 0;
+
         while (true) {
-            Vector<Integer> parent = new Vector<>(vertexCount);
-            for (int i = 0; i < vertexCount; i++) {
-                parent.add(-1);
-            }
-            Queue<Integer> q = new LinkedList<>();
-            parent.set(source, source);
-            q.add(source);
-            while (!q.isEmpty() && parent.get(sink) == -1) {
-                int here = q.peek();
-                q.poll();
-                for (int there = 0; there < vertexCount; ++there) {
-                    if (capacity[here][there] - flow[here][there] > 0 && parent.get(there) == -1) {
-                        q.add(there);
-                        parent.set(there, here);
+            int[] parent = new int[vertexCount];
+            boolean[] visited = new boolean[vertexCount];
+            Queue<Integer> queue = new LinkedList<>();
+
+            queue.add(source);
+            visited[source] = true;
+            parent[source] = -1;
+
+            while (!queue.isEmpty() && !visited[sink]) {
+                int current = queue.poll();
+
+                for (int next = 0; next < vertexCount; next++) {
+                    if (!visited[next] && capacity[current][next] - flow[current][next] > 0) {
+                        queue.add(next);
+                        visited[next] = true;
+                        parent[next] = current;
                     }
                 }
             }
-            if (parent.get(sink) == -1) {
-                break;
+
+            if (!visited[sink]) {
+                break; // No more augmenting paths
             }
 
-            int amount = INF;
-            String printer = "path : ";
-            StringBuilder sb = new StringBuilder();
-            for (int p = sink; p != source; p = parent.get(p)) {
-                amount = Math.min(capacity[parent.get(p)][p] - flow[parent.get(p)][p], amount);
-                sb.append(p + "-");
+            int pathFlow = INF;
+            for (int v = sink; v != source; v = parent[v]) {
+                int u = parent[v];
+                pathFlow = Math.min(pathFlow, capacity[u][v] - flow[u][v]);
             }
-            sb.append(source);
-            for (int p = sink; p != source; p = parent.get(p)) {
-                flow[parent.get(p)][p] += amount;
-                flow[p][parent.get(p)] -= amount;
+
+            for (int v = sink; v != source; v = parent[v]) {
+                int u = parent[v];
+                flow[u][v] += pathFlow;
+                flow[v][u] -= pathFlow;
             }
-            totalFlow += amount;
-            printer += sb.reverse() + " / max flow : " + totalFlow;
-            System.out.println(printer);
+
+            totalFlow += pathFlow;
         }
 
         return totalFlow;

src/test/java/com/thealgorithms/dynamicprogramming/FordFulkersonTest.java

@@ -0,0 +1,94 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class FordFulkersonTest {
+    @Test
+    public void testMaxFlow() {
+        int vertexCount = 6;
+        int[][] capacity = new int[vertexCount][vertexCount];
+        int[][] flow = new int[vertexCount][vertexCount];
+
+        // Setting up the capacity graph
+        capacity[0][1] = 12;
+        capacity[0][3] = 13;
+        capacity[1][2] = 10;
+        capacity[2][3] = 13;
+        capacity[2][4] = 3;
+        capacity[2][5] = 15;
+        capacity[3][2] = 7;
+        capacity[3][4] = 15;
+        capacity[4][5] = 17;
+
+        int maxFlow = FordFulkerson.networkFlow(vertexCount, capacity, flow, 0, 5);
+        assertEquals(23, maxFlow);
+    }
+
+    @Test
+    public void testNoFlow() {
+        int vertexCount = 6;
+        int[][] capacity = new int[vertexCount][vertexCount];
+        int[][] flow = new int[vertexCount][vertexCount];
+
+        // No connections between source and sink
+        capacity[0][1] = 10;
+        capacity[2][3] = 10;
+
+        int maxFlow = FordFulkerson.networkFlow(vertexCount, capacity, flow, 1, 4);
+        assertEquals(0, maxFlow);
+    }
+
+    @Test
+    public void testSinglePath() {
+        int vertexCount = 6;
+        int[][] capacity = new int[vertexCount][vertexCount];
+        int[][] flow = new int[vertexCount][vertexCount];
+
+        // Setting up a single path from source to sink
+        capacity[0][1] = 5;
+        capacity[1][2] = 5;
+        capacity[2][3] = 5;
+        capacity[3][4] = 5;
+        capacity[4][5] = 5;
+
+        int maxFlow = FordFulkerson.networkFlow(vertexCount, capacity, flow, 0, 5);
+        assertEquals(5, maxFlow);
+    }
+
+    @Test
+    public void testParallelPaths() {
+        int vertexCount = 4;
+        int[][] capacity = new int[vertexCount][vertexCount];
+        int[][] flow = new int[vertexCount][vertexCount];
+
+        // Setting up parallel paths from source to sink
+        capacity[0][1] = 10;
+        capacity[0][2] = 10;
+        capacity[1][3] = 10;
+        capacity[2][3] = 10;
+
+        int maxFlow = FordFulkerson.networkFlow(vertexCount, capacity, flow, 0, 3);
+        assertEquals(20, maxFlow);
+    }
+
+    @Test
+    public void testComplexNetwork() {
+        int vertexCount = 5;
+        int[][] capacity = new int[vertexCount][vertexCount];
+        int[][] flow = new int[vertexCount][vertexCount];
+
+        // Complex network
+        capacity[0][1] = 10;
+        capacity[0][2] = 10;
+        capacity[1][3] = 4;
+        capacity[1][4] = 8;
+        capacity[2][4] = 9;
+        capacity[3][2] = 6;
+        capacity[3][4] = 10;
+
+        int maxFlow = FordFulkerson.networkFlow(vertexCount, capacity, flow, 0, 4);
+        assertEquals(19, maxFlow);
+    }
+}