diameter of a Binary tree recursive approach - c++

Question

I am trying to find diameter using recursion ,I am confused with recursion
some of the test cases I tried I got correct answer at some point
Integer overflow occured But Below author's solution was accepted with same data types
My approach:
For every node, length of longest path which pass it = MaxDepth of its left subtree + MaxDepth of its right subtree.
My question is whats wrong with my implementation
class Solution {
public:
int mx = 0;
int solve(TreeNode* root) {
if (root == NULL)return 0;
int leftheight = diameterOfBinaryTree(root->left) + 1;
int rightheight = diameterOfBinaryTree(root->right) + 1;
mx = max(mx, leftheight + rightheight);
return max(leftheight, rightheight);
}
int diameterOfBinaryTree(TreeNode* root) {
solve(root);
return mx;
}
};
Authors approach: same approach but different recursion implementation
class Solution {
public:
int maxdiadepth = 0;
int dfs(TreeNode* root) {
if (root == NULL) return 0;
int leftdepth = dfs(root->left);
int rightdepth = dfs(root->right);
if (leftdepth + rightdepth > maxdiadepth) maxdiadepth = leftdepth + rightdepth;
return max(leftdepth + 1, rightdepth + 1);
}
int diameterOfBinaryTree(TreeNode* root) {
dfs(root);
return maxdiadepth;
}
};

Answer 1

In the working implementation, the recursive dfs call returns the max depth of the subtree.
In your implementation, the recursive diameterOfBinaryTree call returns the currently accumulated approximation to the diameter. You assign it to variables named leftheight and rightheight - that's misleading; the value is not, in fact, the height of the left or right sub-tree.

Answer 2

Consider the case when you hit a leaf node or the case where you have only one node. Your algorithm returns 2, which is incorrect. This problem arises because you compute the height by adding one to the left / right subtree, no matter what.
To fix this, add one when you return the height, like so: max(leftheight, rightheight) + 1
Btw, when you recursively call, you should do solve(root->left) or solve(root->right) and not diameterOfBinaryTree(root->left) :P