Balanced Binary Tree——数是否是平衡，即任意节点左右字数高度差不超过1

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.

 /**
  * Definition for binary tree
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     bool isBalanced(TreeNode *root) {
         if(root==NULL) return true;
         int l=height(root->left);
         int r=height(root->right);
         if(l<||r<||l-r>||r-l>) return false;
         return true;
     }
     int height(TreeNode *root){
         if(root==NULL) return ;
         int l=height(root->left);
         int r=height(root->right);
         if(l<||r<||l-r>||r-l>) return -;
         return max(l,r)+;
     }
 };

其他做法：

转自：http://blog.csdn.net/feliciafay/article/details/18348065

// 104ms过大集合
 /**
  * Definition for binary tree
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     int height(TreeNode* root) {
         if(root==NULL)
             return ;
         else{
             int l=height(root->left);
             int r=height(root->right);
             return +((l>r)?l:r);
         }
     }
     bool isBalanced(TreeNode *root) {
         if(root==NULL)
             return true;
         else{
             int l,r;
             l=height(root->left);
             r=height(root->right);
             if((l>r+)||(r>l+))
                 return false;
             else
                 return isBalanced(root->left)&&isBalanced(root->right);
         }
     }
 }; 

 // 68ms过大集合  简洁版
 public:
 int cntHeight(TreeNode *root) {
     if(root == NULL) return ;
     int l = cntHeight(root->left);
     int r = cntHeight(root->right);
     if(l <  || r <  || abs(l-r) > ) return -; //自定义 return -1，表示不平衡的情况
     else  return max(l, r) + ;
 }
 bool isBalanced(TreeNode *root) {
     if(root == NULL) return true;
     int l = cntHeight(root->left);
     int r = cntHeight(root->right);
     if(l <  || r <  || abs(l-r) > ) return false;
     else return true;
 }  

 // 68ms过大集合  更简洁版
 public:
 int cntHeight(TreeNode *root) {
     if(root == NULL) return ;
     int l = cntHeight(root->left);
     int r = cntHeight(root->right);
     if(l <  || r <  || abs(l-r) > ) return -; //自定义 return -1，表示不平衡的情况
     else  return max(l, r) + ;
 }
 bool isBalanced(TreeNode *root) {
     if(root == NULL) return true;
     int l = cntHeight(root->left);
     int r = cntHeight(root->right);
     if(l <  || r <  || abs(l-r) > ) return false;
     else return true;
 }