110. Balanced Binary Tree.cpp

#include <cmath>
using namespace std;
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)
    {
        int h = 0;
        return dfs(root, h);
    }

private:
    bool dfs(TreeNode *node, int &h)
    {
        if (!node)
        {
            h = 0;
            return true;
        }
        int left = 0, right = 0;
        if (!dfs(node->left, left) || !dfs(node->right, right))
        {
            return false;
        }
        if (abs(left - right) > 1)
            return false;
        h = 1 + max(left, right);
        return true;
    }
};