110. Balanced Binary Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();



class Solution 
{
public:   
    const int UNBALANCED=-66;
    bool isBalanced(TreeNode* root) 
    {
        if(root==NULL)
            return true;
        return getHeight(root)!=UNBALANCED;
    }
    
    int getHeight(TreeNode* T)
    {
        if(T==NULL)
            return 0;
        int l=getHeight(T->left);
        int r=getHeight(T->right);
        if(l==UNBALANCED||r==UNBALANCED||abs(l-r)>1)
            return UNBALANCED;
        return 1+max(l,r);
    } 
};

递归判断左右子树，只要有一个节点不平衡，则整棵树不平衡