diff --git a/src/main/java/com/cool/hot100/binary_tree/Num543.java b/src/main/java/com/cool/hot100/binary_tree/Num543.java
index f0abcc5..1f928a9 100644
--- a/src/main/java/com/cool/hot100/binary_tree/Num543.java
+++ b/src/main/java/com/cool/hot100/binary_tree/Num543.java
@@ -11,18 +11,20 @@ package com.cool.hot100.binary_tree;
  */
 public class Num543 {
 
+    int max=0;
     public int diameterOfBinaryTree(TreeNode root) {
         if (root == null) return 0;
         int left = getTreeDeep(root.left);
         int right = getTreeDeep(root.right);
-        return left + right;
+        return Math.max(max,left+right);
     }
 
     private int getTreeDeep(TreeNode root) {
         if (root == null) return 0;
-        int res = getTreeDeep(root.left);
-        res = Math.max(res, getTreeDeep(root.right));
-        return res + 1;
+        int left = getTreeDeep(root.left);
+        int right=getTreeDeep(root.right);
+        max = Math.max(max,left+right );
+        return Math.max(left,right)+1;
     }
 
 }