题目：

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代码(首刷看解析 2024年1月30日）：

class Solution {
public:
    int depth(TreeNode* root) {
        if (root == nullptr) return 0;
        int leftHeight = depth(root->left);
        if (leftHeight == -1) return -1;
        int rightHeight = depth(root->right);
        if (rightHeight == -1) return -1;
        if (abs(leftHeight - rightHeight) > 1) {
            return -1;
        } else {
            return 1 + max(leftHeight,rightHeight);
        }

    }
    bool isBalanced(TreeNode* root) {
        if (root == nullptr) return true;
        return depth(root) == -1 ? false : true;
    }
};