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‎src/main/java/com/eprogrammerz/examples/algorithm/trees/SymmetricBinaryTree.java‎
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‎src/main/java/com/eprogrammerz/examples/algorithm/trees/SymmetricBinaryTree.java‎
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+187Lines changed: 187 additions & 0 deletions
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+package com.eprogrammerz.examples.algorithm.trees;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Find if tree is symmetric
+ */
+public class SymmetricBinaryTree {
+    /**
+     * This is naive solution using level order traversal
+     *
+     * if no node is present, add new node with Integer.MAX_VALUE and see if that particular level is symmetric
+     *
+     * @param A
+     * @return
+     */
+    public int isSymmetric(TreeNode A) {
+        if (A == null) return 1;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(A);
+
+        while(!queue.isEmpty()) {
+            int size = queue.size();
+            List<Integer> level = new ArrayList<>();
+            for (int i = 0; i < size; i++) {
+
+                TreeNode node = queue.poll();
+                level.add(node.val);
+
+                if (node.val != Integer.MAX_VALUE) {
+                    if (node.left != null) {
+                        queue.add(node.left);
+                    } else {
+                        queue.add(new TreeNode(Integer.MAX_VALUE));
+                    }
+
+                    if (node.right != null) {
+                        queue.add(node.right);
+                    } else {
+                        queue.add(new TreeNode(Integer.MAX_VALUE));
+                    }
+                }
+            }
+
+            if (!isBalanced(level)) {
+                return 0;
+            }
+
+        }
+        return 1;
+    }
+
+    private boolean isBalanced(List<Integer> list) {
+        if (list.size() == 1) return true;
+
+        if (list.size() % 2 != 0) return false;
+
+        for (int s = 0, e = list.size() - 1; s < e; s++, e--) {
+            if (!list.get(s).equals(list.get(e))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    @Test
+    public void testSymmetricTree() {
+        /**
+         *                  1
+         *                /   \
+         *               2     2
+         *              /     /
+         *             3     3
+         */
+        TreeNode root = new TreeNode(1);
+        root.left = new TreeNode(2);
+        root.left.left = new TreeNode(3);
+
+        root.right = new TreeNode(2);
+        root.right.left = new TreeNode(3);
+        assertEquals(0, isSymmetric(root));
+
+        /**
+         *                              9
+         *                             /   \
+         *                           10     10
+         *                          /  \   /  \
+         *                         7    5 5   7
+         *                             / \    \
+         *                            8   1    6
+         *                                     /
+         *                                    2
+         *
+         *                        Min Depth = 3
+         */
+        TreeNode root1 = new TreeNode(9);
+        root1.right = new TreeNode(10);
+        root1.left = new TreeNode(10);
+
+        root1.left.left = new TreeNode(7);
+        root1.left.right = new TreeNode(5);
+        root1.right.left = new TreeNode(5);
+        root1.right.right = new TreeNode(7);
+
+        assertEquals(1, isSymmetric(root1));
+        root1.left.right.right = new TreeNode(1);
+
+        root1.right.right.right = new TreeNode(6);
+        root1.right.right.right.left = new TreeNode(2);
+
+        assertEquals(0, isSymmetric(root1));
+    }
+
+    /**
+     * Better solution with recursion
+     *
+     * @param root
+     * @return
+     */
+    int isSymmetricBetter(TreeNode root) {
+        return isSymmetric(root, root) ? 1 : 0;
+    }
+
+    private boolean isSymmetric(TreeNode node1, TreeNode node2) {
+        if (node1 == null && node2 == null) return true;
+
+        if ((node1 == null) || (node2 == null) || node1.val != node2.val) return false;
+
+        return isSymmetric(node1.left, node2.right) && isSymmetric(node1.right, node2.left);
+    }
+
+
+    @Test
+    public void testSymmetricBetterTree() {
+        /**
+         *                  1
+         *                /   \
+         *               2     2
+         *              /     /
+         *             3     3
+         */
+        TreeNode root = new TreeNode(1);
+        root.left = new TreeNode(2);
+        root.left.left = new TreeNode(3);
+
+        root.right = new TreeNode(2);
+        root.right.left = new TreeNode(3);
+        assertEquals(0, isSymmetricBetter(root));
+
+        /**
+         *                              9
+         *                             /   \
+         *                           10     10
+         *                          /  \   /  \
+         *                         7    5 5   7
+         *                             / \    \
+         *                            8   1    6
+         *                                     /
+         *                                    2
+         *
+         *                        Min Depth = 3
+         */
+        TreeNode root1 = new TreeNode(9);
+        root1.right = new TreeNode(10);
+        root1.left = new TreeNode(10);
+
+        root1.left.left = new TreeNode(7);
+        root1.left.right = new TreeNode(5);
+        root1.right.left = new TreeNode(5);
+        root1.right.right = new TreeNode(7);
+
+        assertEquals(1, isSymmetricBetter(root1));
+        root1.left.right.right = new TreeNode(1);
+
+        root1.right.right.right = new TreeNode(6);
+        root1.right.right.right.left = new TreeNode(2);
+
+        assertEquals(0, isSymmetricBetter(root1));
+    }
+}