[Leetcode][Tree][Balanced Binary Tree]

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判斷一棵樹是不是平衡二叉樹，之前做過，還有點印象，用一個函數返回樹的高度，如果是-1的話，就說明子樹不平衡。

1A很開心~

 1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     int height(TreeNode * root) {13         int hleft, hright;14         hleft = hright = 0;15         if (root->left != NULL) {16             hleft = height(root->left);17         }18         if (root->right != NULL) {19             hright = height(root->right);20         }21         if (hleft < 0 || hright < 0 || abs(hleft - hright) > 1) {22             return -1;23         }24         return max(hleft, hright) + 1;25     }26     bool isBalanced(TreeNode *root) {27         if (root == NULL) {28             return true;29         } else {30             return height(root) >= 0;31         }32     }33 };