Java：二进制搜索树递归的最小深度

Question

I am writing the code to calculate minimum depth of binary tree
My solution works well for tree BST if the inputs are 6,4,9,3,5,7,12,2,8
because minimum depth is coming as 3 which is correct.
But when the tree is 3,2 , minimum depth is coming as 1 instead of 2.
My code snippet is:

int minimumHeightRec(TreeNode root)
        {
            if(root == null) return 0;
            int left = minimumHeightRec(root.left);
            int right = minimumHeightRec(root.right);
            if(left > right) return right + 1;
            else return left + 1;
        }

Answer 1

Your implementation is correct. The expected minHeight should be 1 instead of 2. Consider your example of [3, 2] the BST may have the following form:

  3
 /
2

looking into left of root has height of 2: (3) -> (2)

looking into right of root has height of 1: (3)

You're looking for the minHeight of the BST, so taking the right branch of height 1 is the correct choice.

Note that you may have a different tree form where 2 is the root, but the logic and result will be the same.

Answer 2

• The else is useless because there is a return in the if.
• Some more code (TreeNode class and main) would be usefull.