530. Minimum Absolute Difference in BST

• Difficulty: Easy

• Topics: Tree

• Similar Questions:

  • K-diff Pairs in an Array

Problem:

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

Example:

Input:

   1
    \
     3
    /
   2

Output:
1

Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

Note: There are at least two nodes in this BST.

Solutions:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int getMinimumDifference(TreeNode* root) {
        vector<int> last;
        int ret = INT_MAX;
        helper(root, last, ret);
        return ret;
    }

private:
    void helper(TreeNode* root, vector<int>& last, int& ret) {
        if (root == nullptr)    return;
        helper(root->left, last, ret);

        if (last.size() == 0) {
            last.push_back(root->val);
        } else {
            ret = min(ret, abs(last.back() - root->val));
            last.back() = root->val;
        }

        helper(root->right, last, ret);
    }

};