SymmetricTree

Change-Id: Ib4dece75b87b545c5f1a1fde03ce54717a3c912a

Author: applewjg

SymmetricTree.java

@@ -0,0 +1,46 @@
+/*
+ Author:     King, [email protected]
+ Date:       Dec 25, 2014
+ Problem:    Symmetric Tree
+ Difficulty: Easy
+ Source:     https://oj.leetcode.com/problems/symmetric-tree/
+ Notes:
+ Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
+ For example, this binary tree is symmetric:
+     1
+    / \
+   2   2
+  / \ / \
+ 3  4 4  3
+ But the following is not:
+    1
+   / \
+  2   2
+   \   \
+   3    3
+ Note:
+ Bonus points if you could solve it both recursively and iteratively.
+
+ Solution: 1. Recursive solution
+ */
+
+/**
+ * Definition for binary tree
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public boolean isSymmetric(TreeNode root) {
+        if (root == null) return true;
+        return solve (root.left, root.right);
+    }
+    public boolean solve(TreeNode t1, TreeNode t2) {
+        if (t1 == null && t2 == null) return true;
+        if (t1 == null && t2 != null || t1 != null && t2 == null || t1.val != t2.val) return false;
+        return solve(t1.left, t2.right) && solve(t1.right, t2.left);
+    }
+}