Merge Algorithm\Balance into Algorithm\Flow

Author: clue

src/Balance.php

@@ -74,4 +74,44 @@ public function getFlowVertex(Vertex $vertex)
 
         return $sumOfFlow;
     }
+
+    public function getBalance()
+    {
+        $balance = 0;
+        // Sum for all vertices of value
+        foreach ($this->set->getVertices() as $vertex) {
+            $balance += $vertex->getBalance();
+        }
+
+        return $balance;
+    }
+
+    /**
+     * check if the current flow is balanced (aka "balanced flow" or "b-flow")
+     *
+     * a flow is considered balanced if each edge's current flow does not exceed its
+     * maximum capacity (which is always guaranteed due to the implementation
+     * of Edge::setFlow()) and each vertices' flow (i.e. outflow-inflow) equals
+     * its balance.
+     *
+     * checking whether the FLOW is balanced is not to be confused with checking
+     * whether the GRAPH is balanced (see Graph::isBalanced() instead)
+     *
+     * @return boolean
+     * @see Algorithm\Degree::isBalanced() if you merely want to check indegree=outdegree
+     * @uses self::getFlowVertex()
+     * @uses Vertex::getBalance()
+     */
+    public function isBalancedFlow()
+    {
+        // no need to check for each edge: flow <= capacity (setters already check that)
+        // check for each vertex: outflow-inflow = balance
+        foreach ($this->set->getVertices() as $vertex) {
+            if ($this->getFlowVertex($vertex) !== $vertex->getBalance()) {
+                return false;
+            }
+        }
+
+        return true;
+    }
 }

src/Flow.php

@@ -12,6 +12,8 @@ public function testGraphEmpty()
         $alg = new AlgorithmFlow($graph);
 
         $this->assertFalse($alg->hasFlow());
+        $this->assertEquals(0, $alg->getBalance());
+        $this->assertTrue($alg->isBalancedFlow());
 
         return $graph;
     }
@@ -59,4 +61,17 @@ public function testGraphWithUnweightedEdges(Graph $graph)
 
         $this->assertTrue($alg->hasFlow());
     }
+
+    public function testGraphBalance()
+    {
+        // source(+100) -> sink(-10)
+        $graph = new Graph();
+        $graph->createVertex('source')->setBalance(100);
+        $graph->createVertex('sink')->setBalance(-10);
+
+        $alg = new AlgorithmFlow($graph);
+
+        $this->assertEquals(90, $alg->getBalance());
+        $this->assertFalse($alg->isBalancedFlow());
+    }
 }