[LeetCode] 110. Balanced Binary Tree 解题思路

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.

问题：给定一个二叉树，判断其是否平衡。

当二叉树中所有节点的左右子树高度差不大于 1 时，这个二叉树视为平衡二叉树。

解题思路应该算一种分治思想。根据定义，递归地判断，实现判断。

     const int unbalanceKids = -;

     /**
      * count the number of children of node and itself
      */
     int height(TreeNode* node){

         int heightL = ;
         if (node->left != NULL){
             heightL = height(node->left);
         }

         if(heightL == unbalanceKids){
             return unbalanceKids;
         }

         int heightR = ;
         if (node->right != NULL){
             heightR = height(node->right);
         }

         if(heightR == unbalanceKids){
             return unbalanceKids;
         }

         if (abs(heightL - heightR) > ){
             return unbalanceKids;
         }

         return max(heightL, heightR) + ;
     }

     bool isBalanced(TreeNode* root) {

         if (root == NULL){
             return true;
         }

         int res  = height(root);
         if (res == unbalanceKids){
             return false;
         }

         return true;
     }