Bipartite Graph BFS

Author: akashdeep023

34-Graphs_(Part-II)/GraphsP2_Bipartite.java

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+import java.util.ArrayList;
+import java.util.Queue;
+import java.util.LinkedList;
+
+public class GraphsP2_Bipartite {
+    static class Edge {
+        int src, dest;
+
+        public Edge(int src, int dest) {
+            this.src = src;
+            this.dest = dest;
+        }
+    }
+
+    static void createGraph(ArrayList<Edge>[] graph) {
+        /*
+         * 1 ———— 0 ———— 2
+         *  \           /
+         *   \         /
+         *    3 ————— 4
+         */
+        for (int i = 0; i < graph.length; i++) {
+            graph[i] = new ArrayList<>();
+        }
+        graph[0].add(new Edge(0, 1));
+        graph[0].add(new Edge(0, 2));
+
+        graph[1].add(new Edge(1, 0));
+        graph[1].add(new Edge(1, 3));
+
+        graph[2].add(new Edge(2, 0));
+        graph[2].add(new Edge(2, 4));
+
+        graph[3].add(new Edge(3, 1));
+        graph[3].add(new Edge(3, 4));
+
+        graph[4].add(new Edge(4, 2));
+        graph[4].add(new Edge(4, 3));
+    }
+
+    // Bipartite Graph BFS -------------------------------- TC -> O(V+E) & SC -> O(V) where V is vertex & E is edge
+    public static boolean isBipartiteGraph(ArrayList<Edge>[] graph) {
+        int[] colors = new int[graph.length];
+        for (int i = 0; i < colors.length; i++) {
+            colors[i] = -1; // no colors
+        }
+        for (int i = 0; i < graph.length; i++) {
+            if (colors[i] == -1) {
+                if (isBipartiteGraphUtil(graph, i, colors)) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    public static boolean isBipartiteGraphUtil(ArrayList<Edge>[] graph, int curr, int[] colors) { // BSF
+        Queue<Integer> q = new LinkedList<>();
+        q.add(curr); // add in queue
+        colors[curr] = 0; // add color (Yellow)
+        while (!q.isEmpty()) {
+            curr = q.remove();
+            for (int level = 0; level < graph[curr].size(); level++) { // current Edge neighbor traversal
+                Edge e = graph[curr].get(level);
+                if (colors[e.dest] == colors[curr]) { // same color
+                    return false;
+                } else if (colors[e.dest] == -1) { // add color
+                    q.add(e.dest);
+                    colors[e.dest] = (colors[curr] == 0) ? 1 : 0;
+                }
+                // deffered color -> continue
+            }
+        }
+        return true;
+    }
+
+    public static void main(String[] args) {
+        // Bipartite Graph --------------------------------
+        // If graph doesn't have cycle -> Bipartite Graph (true)
+        int V = 5;
+        @SuppressWarnings("unchecked") // Remove unnecessary warnings
+        ArrayList<Edge>[] graph = new ArrayList[V];
+        createGraph(graph);
+        System.out.println("Is Bipartite graph : " + isBipartiteGraph(graph));
+    }
+}