Create zero_one_bfs.java

Author: ananya-research

src/main/java/com/thealgorithms/graph/zero_one_bfs.java

@@ -0,0 +1,53 @@
+package com.thealgorithms.graphs;
+
+import java.util.*;
+
+/**
+ * 0-1 BFS for shortest paths on graphs with 0/1 edge weights.
+ *
+ * <p>Time: O(V + E). Space: O(V).
+ *
+ * <p>References:
+ * <ul>
+ *   <li>https://cp-algorithms.com/graph/01_bfs.html</li>
+ * </ul>
+ */
+public final class ZeroOneBfs {
+
+    private ZeroOneBfs() {
+        // utility class
+    }
+
+    /**
+     * Computes shortest distances from {@code src} in a graph with edges weighted 0 or 1.
+     *
+     * @param n number of vertices labeled [0..n-1]
+     * @param edges adjacency list where each entry is (to, weight) with weight ∈ {0,1}
+     * @param src source vertex
+     * @return distances array; {@code Integer.MAX_VALUE} if unreachable
+     */
+    public static int[] shortestPaths(int n, List<List<int[]>> edges, int src) {
+        int[] dist = new int[n];
+        Arrays.fill(dist, Integer.MAX_VALUE);
+        Deque<Integer> dq = new ArrayDeque<>();
+        dist[src] = 0;
+        dq.addFirst(src);
+
+        while (!dq.isEmpty()) {
+            int u = dq.pollFirst();
+            for (int[] e : edges.get(u)) {
+                int v = e[0], w = e[1];
+                int nd = dist[u] + w;
+                if (nd < dist[v]) {
+                    dist[v] = nd;
+                    if (w == 0) {
+                        dq.addFirst(v);
+                    } else {
+                        dq.addLast(v);
+                    }
+                }
+            }
+        }
+        return dist;
+    }
+}