文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

Minimum Absolute Difference in BST

2. Solution

• Version 1

/**
 * 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> values;
        inOrderTranverse(root, values);
        int min = INT_MAX;
        for(int i = 1; i < values.size(); i++) {
            int diff = values[i] - values[i - 1];
            if(min > diff) {
                min = diff;
            }
        }
        return min;
    }
    
private:
    void inOrderTranverse(TreeNode* root, vector<int>& values) {
        if(!root) {
            return;
        }
        if(root->left) {
            inOrderTranverse(root->left, values);
        }
        values.push_back(root->val);
        if(root->right) {
            inOrderTranverse(root->right, values);
        }
    }
};

• Version 2

/**
 * 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) {
        int min = INT_MAX;
        int current = -1;
        inOrderTranverse(root, min, current);
        return min;
    }
    
private:
    void inOrderTranverse(TreeNode* root, int& min, int& current) {
        if(!root) {
            return;
        }
        if(root->left) {
            inOrderTranverse(root->left, min, current);
        }
        if(current != -1) {
            if(min > root->val - current) {
                min = root->val - current;
            }
        }
        current = root->val;
        if(root->right) {
            inOrderTranverse(root->right, min, current);
        }
    }
};

Reference

1. https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/