代码随想录：平衡二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if (!root)
            return true;
        if (getDepth(root->left) == -1 || getDepth(root->right)==-1){return false;}
        if (abs(getDepth(root->left) - getDepth(root->right)) > 1) {
            return false;
        } else {
            return true;
        }
    }

    int getDepth(TreeNode* node) {
        if (!node) {
            return 0;
        }
        int left = getDepth(node->left);
        int right = getDepth(node->right);
        if (left == -1 || right == -1) {
            return -1;
        }
        if (abs(left - right) > 1) {
            return -1;
        }
        return max(left, right) + 1;
    }
};