feat: Add Stoer-Wagner Algorithm for Minimum Cut (#6752)

* feat: Add Stoer-Wagner Algorithm for Minimum Cut

* fix: Correct Stoer-Wagner implementation

* fix: Remove unused import

* fix: Apply clang-format

src/test/java/com/thealgorithms/graph/StoerWagnerTest.java

@@ -0,0 +1,64 @@
+package com.thealgorithms.graph;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the StoerWagner global minimum cut algorithm.
+ *
+ * These tests verify correctness of the implementation across
+ * several graph configurations: simple, complete, disconnected,
+ * and small edge cases.
+ */
+public class StoerWagnerTest {
+
+    @Test
+    public void testSimpleGraph() {
+        int[][] graph = {{0, 3, 2, 0}, {3, 0, 1, 4}, {2, 1, 0, 5}, {0, 4, 5, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(5, algo.findMinCut(graph)); // Correct minimum cut = 5
+    }
+
+    @Test
+    public void testTriangleGraph() {
+        int[][] graph = {{0, 2, 3}, {2, 0, 4}, {3, 4, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(5, algo.findMinCut(graph)); // min cut = 5
+    }
+
+    @Test
+    public void testDisconnectedGraph() {
+        int[][] graph = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(0, algo.findMinCut(graph)); // Disconnected graph => cut = 0
+    }
+
+    @Test
+    public void testCompleteGraph() {
+        int[][] graph = {{0, 1, 1, 1}, {1, 0, 1, 1}, {1, 1, 0, 1}, {1, 1, 1, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(3, algo.findMinCut(graph)); // Each vertex connected to all others
+    }
+
+    @Test
+    public void testSingleVertex() {
+        int[][] graph = {{0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(0, algo.findMinCut(graph)); // Only one vertex
+    }
+
+    @Test
+    public void testTwoVertices() {
+        int[][] graph = {{0, 7}, {7, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(7, algo.findMinCut(graph)); // Only one edge, cut weight = 7
+    }
+
+    @Test
+    public void testSquareGraphWithDiagonal() {
+        int[][] graph = {{0, 2, 0, 2}, {2, 0, 3, 0}, {0, 3, 0, 4}, {2, 0, 4, 0}};
+        StoerWagner algo = new StoerWagner();
+        assertEquals(4, algo.findMinCut(graph)); // verified manually
+    }
+}