update the problem "Balanced Binary Tree"

Author: haoel

src/balancedBinaryTree/balancedBinaryTree.cpp

@@ -25,21 +25,51 @@ class Solution {
 public:
     bool isBalanced(TreeNode *root) {
         int height=0;
-        return isBalancedUtil(root,&height);
+        return isBalancedUtil(root, height);
     }
-    bool isBalancedUtil(TreeNode* root,int *height){
+
+    bool isBalancedUtil(TreeNode* root, int& height){
        if(root==NULL){
-          *height=0;
-          return 1;
+          height=0;
+          return true;
        }
-       int lh=0,rh=0;
-       bool isLeft,isRight;
-       isLeft=isBalancedUtil(root->left,&lh);
-       isRight=isBalancedUtil(root->right,&rh);
-       *height=(lh>rh?lh:rh)+1;
-       if(abs(lh-rh)>1)
-          return 0;
-       return isLeft&&isRight;
+       int lh=0, rh=0;
+       bool isLeft = isBalancedUtil(root->left, lh);
+       bool isRight = isBalancedUtil(root->right, rh);
+       height = (lh > rh ? lh : rh) + 1;
+       return (abs(lh-rh)<=1 && isLeft && isRight);
+    }
+
+};
+
+//Notes: 
+// I think the above solution should be more efficent than the below, 
+//  but for leetcode, the below solution needs 60ms, the above needs 88ms
+class Solution {
+public:
+    bool isBalanced(TreeNode *root) {
+        if (root==NULL) return true;
+        
+        int left = treeDepth(root->left); 
+        int right = treeDepth(root->right);
+        
+        if (left-right>1 || left-right < -1) {
+            return false;
+        }
+        return isBalanced(root->left) && isBalanced(root->right);
+    }
+    
+    int treeDepth(TreeNode *root) {
+        if (root==NULL){
+            return 0;
+        }
+
+        int left=1, right=1;
+        
+        left += treeDepth(root->left);
+        right += treeDepth(root->right);
+        
+        return left>right?left:right;
     }
 
 };