110_Balanced_Binary_Tree

Brute Force
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    int getDepth(TreeNode* node){
        if (node == NULL) return 0;
        return max(getDepth(node->left), getDepth(node->right)) + 1;
    }
    bool helper(TreeNode* node){
        if (node == NULL) return true;
        int left1 = getDepth(node->left);
        int right1 = getDepth(node->right);
        return abs(right1 - left1) <= 1 && helper(node->left) && helper(node->right);
    }
public:
    bool isBalanced(TreeNode* root) {
        if (root == NULL) return true;
        return helper(root);
    }
};

Calculate depth + checking
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    bool result = true;
    int getDepth(TreeNode* node){
        if (node == NULL) return 0;
        int left1 = getDepth(node->left);
        int right1 = getDepth(node->right);
        if (abs(left1 - right1) > 1) result = false;
        return max(left1, right1) + 1;
    }
public:
    bool isBalanced(TreeNode* root) {
        if (root == NULL) return true;
        int trash = getDepth(root);
        return result;
    }
};