Add Solution3.java to problems 0101

Author: huaxu1024

solution/0101.Symmetric Tree/Solution3.java

@@ -0,0 +1,34 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+import java.util.*;
+
+class Solution {
+    public boolean isSymmetric(TreeNode root) {
+        if (root == null) return true;
+        LinkedList<TreeNode> queueA = new LinkedList<>();
+        LinkedList<TreeNode> queueB = new LinkedList<>();
+        queueA.addLast(root);
+        queueB.addLast(root);
+        while (!queueA.isEmpty() && !queueB.isEmpty()) {
+            TreeNode popA = queueA.pollFirst();
+            TreeNode popB = queueB.pollFirst();
+            if (popA == null && popB == null) continue;
+            if (popA == null || popB == null) return false;
+
+            if (popA.val != popB.val) return false;
+            queueA.addLast(popA.left);
+            queueA.addLast(popA.right);
+
+            queueB.addLast(popB.right);
+            queueB.addLast(popB.left);
+        }
+        return queueA.isEmpty() && queueB.isEmpty();
+    }
+}