Update 二叉树相关.md

blogs/Algorithm/剑指 Offer/二叉树相关.md

@@ -236,3 +236,59 @@ class Solution {
 }
 ```
 
+#### [55 - II. 平衡二叉树](https://leetcode-cn.com/problems/ping-heng-er-cha-shu-lcof/)
+
+```java
+class Solution {
+
+    public boolean isBalanced(TreeNode root) {
+        if (root == null) {
+            return true;
+        }
+        Deque<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        while (!queue.isEmpty()) {
+            TreeNode node = queue.poll();
+            int offset = Math.abs(maxDepth(node.left) - maxDepth(node.right));
+            if (offset > 1) {
+                return false;
+            }
+            if (node.left != null) {
+                queue.add(node.left);
+            }
+            if (node.right != null) {
+                queue.add(node.right);
+            }
+        }
+        return true;
+    }
+
+    private int maxDepth(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
+    }
+}
+```
+
+```java
+class Solution {
+
+    public boolean isBalanced(TreeNode root) {
+        if (root == null) {
+            return true;
+        }
+        return Math.abs(maxDepth(root.left) - maxDepth(root.right)) <= 1 && isBalanced(root.left) && isBalanced(
+                root.right);
+    }
+
+    private int maxDepth(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
+    }
+}
+```
+