Create zero_one_bfs.java (#6560)

* Create zero_one_bfs.java

* Rename zero_one_bfs.java to ZeroOneBfs.java

* Update ZeroOneBfs.java

* Update ZeroOneBfs.java

* Create ZeroOneBfsTest.java

* Update ZeroOneBfsTest.java

---------

Co-authored-by: a <alexanderklmn@gmail.com>

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

@@ -0,0 +1,68 @@
+package com.thealgorithms.graph;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class ZeroOneBfsTest {
+
+    // Helper to build adjacency list with capacity n
+    private static List<List<int[]>> makeAdj(int n) {
+        List<List<int[]>> adj = new ArrayList<>(n);
+        for (int i = 0; i < n; i++) {
+            adj.add(new ArrayList<>());
+        }
+        return adj;
+    }
+
+    @Test
+    void simpleLineGraph() {
+        int n = 4;
+        List<List<int[]>> adj = makeAdj(n);
+        // 0 --0--> 1 --1--> 2 --0--> 3
+        adj.get(0).add(new int[] {1, 0});
+        adj.get(1).add(new int[] {2, 1});
+        adj.get(2).add(new int[] {3, 0});
+
+        int[] dist = ZeroOneBfs.shortestPaths(n, adj, 0);
+        assertArrayEquals(new int[] {0, 0, 1, 1}, dist);
+    }
+
+    @Test
+    void parallelEdgesPreferZero() {
+        int n = 3;
+        List<List<int[]>> adj = makeAdj(n);
+        // Two edges 0->1: weight 1 and weight 0. Algorithm should choose 0.
+        adj.get(0).add(new int[] {1, 1});
+        adj.get(0).add(new int[] {1, 0});
+        adj.get(1).add(new int[] {2, 1});
+
+        int[] dist = ZeroOneBfs.shortestPaths(n, adj, 0);
+        assertArrayEquals(new int[] {0, 0, 1}, dist);
+    }
+
+    @Test
+    void unreachableNodes() {
+        int n = 3;
+        List<List<int[]>> adj = makeAdj(n);
+        adj.get(0).add(new int[] {1, 0});
+        int[] dist = ZeroOneBfs.shortestPaths(n, adj, 0);
+        // node 2 unreachable -> Integer.MAX_VALUE
+        assertArrayEquals(new int[] {0, 0, Integer.MAX_VALUE}, dist);
+    }
+
+    @Test
+    void invalidArgs() {
+        int n = 2;
+        List<List<int[]>> adj = makeAdj(n);
+        // invalid weight
+        adj.get(0).add(new int[] {1, 2});
+        assertThrows(IllegalArgumentException.class, () -> ZeroOneBfs.shortestPaths(n, adj, 0));
+        // invalid src
+        assertThrows(IllegalArgumentException.class, () -> ZeroOneBfs.shortestPaths(n, adj, -1));
+        assertThrows(IllegalArgumentException.class, () -> ZeroOneBfs.shortestPaths(n, adj, 2));
+    }
+}