剑指offer系列- 55 II 平衡二叉树

class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(root == nullptr)
            return true;
        // 先判断根节点，再递归判断左右子树
        return balanced(root) && isBalanced(root->left) && isBalanced(root->right);
    }
    int balanced(TreeNode* root){
        if(root == nullptr)
            return 0;
        int left = balanced(root->left);
        int right = balanced(root->right);
        return abs(left-right)>1 ? 0 : max(left,right)+1;
    }
};