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refactor: FordFulkerson (#5384)

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Alex Klymenko 2024-08-25 09:07:02 +02:00 committed by GitHub
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2 changed files with 128 additions and 56 deletions
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92
src/main/java/com/thealgorithms/dynamicprogramming/FordFulkerson.java
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@ -2,76 +2,54 @@ package com.thealgorithms.dynamicprogramming;
import java.util.LinkedList; import java.util.LinkedList;
import java.util.Queue; import java.util.Queue;
import java.util.Vector;
public final class FordFulkerson { public final class FordFulkerson {
private static final int INF = Integer.MAX_VALUE;
private FordFulkerson() { private FordFulkerson() {
} }
static final int INF = 987654321; public static int networkFlow(int vertexCount, int[][] capacity, int[][] flow, int source, int sink) {
// edges
static int vertexCount;
static int[][] capacity;
static int[][] flow;
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 static int networkFlow(int source, int sink) {
flow = new int[vertexCount][vertexCount];
int totalFlow = 0; int totalFlow = 0;
while (true) { while (true) {
Vector<Integer> parent = new Vector<>(vertexCount); int[] parent = new int[vertexCount];
for (int i = 0; i < vertexCount; i++) { boolean[] visited = new boolean[vertexCount];
parent.add(-1); Queue<Integer> queue = new LinkedList<>();
}
Queue<Integer> q = new LinkedList<>(); queue.add(source);
parent.set(source, source); visited[source] = true;
q.add(source); parent[source] = -1;
while (!q.isEmpty() && parent.get(sink) == -1) {
int here = q.peek(); while (!queue.isEmpty() && !visited[sink]) {
q.poll(); int current = queue.poll();
for (int there = 0; there < vertexCount; ++there) {
if (capacity[here][there] - flow[here][there] > 0 && parent.get(there) == -1) { for (int next = 0; next < vertexCount; next++) {
q.add(there); if (!visited[next] && capacity[current][next] - flow[current][next] > 0) {
parent.set(there, here); queue.add(next);
visited[next] = true;
parent[next] = current;
} }
} }
} }
if (parent.get(sink) == -1) {
break;
}
int amount = INF; if (!visited[sink]) {
String printer = "path : "; break; // No more augmenting paths
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 + "-");
} }
sb.append(source);
for (int p = sink; p != source; p = parent.get(p)) { int pathFlow = INF;
flow[parent.get(p)][p] += amount; for (int v = sink; v != source; v = parent[v]) {
flow[p][parent.get(p)] -= amount; int u = parent[v];
pathFlow = Math.min(pathFlow, capacity[u][v] - flow[u][v]);
} }
totalFlow += amount;
printer += sb.reverse() + " / max flow : " + totalFlow; for (int v = sink; v != source; v = parent[v]) {
System.out.println(printer); int u = parent[v];
flow[u][v] += pathFlow;
flow[v][u] -= pathFlow;
}
totalFlow += pathFlow;
} }
return totalFlow; return totalFlow;

94
src/test/java/com/thealgorithms/dynamicprogramming/FordFulkersonTest.java Normal file
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@ -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);
}
}