LeetCode 110. Balanced Binary Tree

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 ofevery node never differ by more than 1.

Just follow the definition.....

    static int getDepth(TreeNode* root) {
        if(!root) return 0;
        return 1 + max(getDepth(root->left), getDepth(root->right));
    }
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        int leftDepth = getDepth(root->left);
        int rightDepth = getDepth(root->right);
        return abs(leftDepth - rightDepth) <= 1 && isBalanced(root->right) && isBalanced(root->left);
    }

For a better performance. It is good to build a data structure. To traversal the tree in bottom up order which might help to end the program earlier once detected unbalanced.

/*
  Build a structure
*/
class BalanceStatsWithHeight {
  bool balanced;
  int height;
}

BalanceStatsWithHeight checkBalanceTree(TreeNode* root) {
  if(!root) return {true, -1};
  auto left_tree = checkBalanceTree(root->left);
  if(!left_tree.balanced) return {false, 0};

  auto right_tree = checkBalanceTree(root->right);
  if(!right_tree.balanced) return {false, 0};

  bool is_balance = abs(left_tree.height - right_tree.height) <= 1;
  int curr_height = max(left_tree.height, right_tree.height) + 1;
  return {is_balance, curr_height};
}