783

783. Minimum Distance Between BST Nodes (Medium)

Given a Binary Search Tree (BST) with the root node root, return the minimum difference between the values of any two different nodes in the tree.

Example :

Input: root = [4,2,6,1,3,null,null]
Output: 1
Explanation:
Note that root is a TreeNode object, not an array.

The given tree [4,2,6,1,3,null,null] is represented by the following diagram:

      4
    /   \
  2      6
 / \    
1   3  

while the minimum difference in this tree is 1, it occurs between node 1 and node 2, also between node 3 and node 2.

Note:

1. The size of the BST will be between 2 and 100.
2. The BST is always valid, each node's value is an integer, and each node's value is different.

Solution 1.

// OJ: https://leetcode.com/problems/minimum-distance-between-bst-nodes/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(log(N))
class Solution {
private:
    int ans = INT_MAX;
    TreeNode *prev = NULL;
    void inorder(TreeNode *root) {
        if (!root) return;
        inorder(root->left);
        if (prev) ans = min(ans, root->val - prev->val);
        prev = root;
        inorder(root->right);
    }
public:
    int minDiffInBST(TreeNode* root) {
        inorder(root);
        return ans;
    }
};