Balanced Binary Tree

原题

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

判断一棵树是否是平衡二叉树，

注意的问题

　　　　　　1）：递归判断左右子树的平衡性(第12行)

　　　　　　2）：左右子树高度相差大于1，而不是等于2，这不是生成平衡树(第10行)

　　　　　　3）：平衡树是不是搜索树？这是一个问题。。。

 1  class Solution 
 2   {
 3   public:
 4       bool isBalanced(TreeNode* root) 
 5           {
 6               if (root == NULL)
 7                   return true;
 8                int lh = height(root->left);
 9               int rh = height(root->right);
10              if(lh - rh > 1 || rh - lh > 1)
11                  return false;
12              return isBalanced(root->left)&&isBalanced(root->right);
13          }
14  //求节点高度
15      int height(TreeNode* &pos)
16      {
17          if(pos == NULL)
18              return -1;
19        //返回节点高度
20          return max(height(pos->left),height(pos->right)) + 1; 
21      }
22  };

 1 class Solution 
 2  {
 3  public:
 4      bool isBalanced(TreeNode* root) 
 5      {
 6          if (root == NULL)
 7              return true;
 8          bool IsSearch = true;
 9          int lh = height(root->left,IsSearch);
10          int rh = height(root->right,IsSearch);
11          if(lh - rh == 2 || rh - lh == 2 || !IsSearch)
12              return false;
13          return true;
14      }
15      //求节点高度
16      int height(TreeNode* &pos,bool &charge)
17      {
18          if(pos == NULL)
19              return -1;
20          if (pos->right != NULL)
21          {
22              if(pos->val >= pos->right->val)
23              {
24                  charge = false;
25                  return 0;
26              }
27          }
28          else if(pos->left != NULL)
29          {
30              if(pos->val <= pos->left->val)
31              {
32                  charge = false;
33                  return 0;
34              }
35          }
36          if(charge)
37              return max(height(pos->left,charge),height(pos->right,charge)) + 1; 
38          else
39              return 0;
40      }
41  };

错误代码