Added solution to find if a tree is subtree of given tree

YogenRaii · YogenRaii · commit 4ea314dba078 · 2019-06-06T07:42:22.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/trees/CheckSubtree.java b/src/main/java/com/eprogrammerz/examples/algorithm/trees/CheckSubtree.java
@@ -0,0 +1,53 @@
+package com.eprogrammerz.examples.algorithm.trees;
+
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertFalse;
+import static junit.framework.TestCase.assertTrue;
+
+public class CheckSubtree {
+
+    @Test
+    public void testSubtree() {
+
+        /**
+         *          10
+         *       /     \
+         *     7         12
+         *   /   \        \
+         *  4     8        15
+         *                  \
+         *                   17
+         *
+         */
+
+        Node root = new Node(10);
+        root.left = new Node(7);
+        root.right = new Node(12);
+        root.left.left = new Node(4);
+        root.left.right = new Node(8);
+        root.right.right = new Node(15);
+        root.right.right.right = new Node(17);
+
+        /**
+         *     7
+         *   /   \
+         *  4     8
+         */
+        Node that = new Node(7);
+        that.left = new Node(4);
+        that.right = new Node(8);
+
+        assertTrue(root.isSubtree(that));
+
+        /**
+         *     7
+         *   /   \
+         *  4     8
+         *   \
+         *    10
+         */
+        that.left.right = new Node(10);
+        assertFalse(root.isSubtree(that));
+    }
+}
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/trees/Node.java b/src/main/java/com/eprogrammerz/examples/algorithm/trees/Node.java
@@ -1,5 +1,8 @@
 package com.eprogrammerz.examples.algorithm.trees;
 
+import java.util.LinkedList;
+import java.util.Queue;
+
 public class Node {
     int data;
     Node left, right;
@@ -60,6 +63,64 @@ public boolean validate() {
         return true;
     }
 
+    /**
+     * Checks if tree is subtree of current tree
+     *
+     * @return true if tree is subtree, else false
+     */
+    public boolean isSubtree(Node that) {
+        // do bfs on this
+        // if node found same as of that.root
+        // then clear the queue of tree
+        // start bfs for both, each queue poll should match
+
+        if (that == null) return false;
+
+        Queue<Node> thisQueue = new LinkedList<>();
+        thisQueue.add(this);
+
+        while (!thisQueue.isEmpty()) {
+            Node thisNode = thisQueue.poll();
+
+            if (thisNode.data == that.data) {
+                return isSubtree(thisNode, that);
+            }
+
+            if (thisNode.left != null) {
+                thisQueue.add(thisNode.left);
+            }
+
+            if (thisNode.right != null) {
+                thisQueue.add(thisNode.right);
+            }
+        }
+
+        return false;
+    }
+
+    private boolean isSubtree(Node t1, Node t2) {
+
+        Queue<Node> t1Queue = new LinkedList<>();
+        t1Queue.add(t1);
+
+        Queue<Node> t2Queue = new LinkedList<>();
+        t2Queue.add(t2);
+
+        while (!t1Queue.isEmpty() && !t2Queue.isEmpty()) {
+            Node t1Node = t1Queue.poll();
+            Node t2Node = t2Queue.poll();
+
+            if (t1Node.data != t2Node.data) return false;
+
+            if (t1Node.left != null) t1Queue.add(t1Node.left);
+            if (t1Node.right != null) t1Queue.add(t1Node.right);
+
+            if (t2Node.left != null) t2Queue.add(t2Node.left);
+            if (t2Node.right != null) t2Queue.add(t2Node.right);
+        }
+        return t1Queue.isEmpty() && t2Queue.isEmpty();
+    }
+
     @Override
     public String toString() {
         return "(" + data + ")";
