Balanced Binary Tree

Q：

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

A:

递归求高度，不知道非递归怎么搞，遗憾。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
 public:
  bool isBalanced(TreeNode *root) {
    int length = 0;
    return isBalancedInternal(root, &length);
  } 
 private:
  bool isBalancedInternal(TreeNode* root, int* length) {
    if (!root) {
      *length = 0;
      return true;
    }
    int l_len, r_len;
    if (!isBalancedInternal(root->left, &l_len) ||
        !isBalancedInternal(root->right, &r_len) ||
        abs(l_len - r_len) > 1) {
      return false;
    }
    *length = max(l_len, r_len) + 1;
    return true;
  }
};