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###### tags: `Leetcode`

# 783. Minimum Distance Between BST Nodes

###### Link : https://leetcode.com/problems/minimum-distance-between-bst-nodes/description/

## 題目
找任兩個node最小的差
## 程式碼 (with inorder list)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDiffInBST(TreeNode* root) {
        inorder.clear();
        inorderRec(root);//inorder recursion(inorder可由小到大)
        int ans = inorder[1] - inorder[0];
        for(int i = 2;i < inorder.size();++i){//找最小差異
            if(inorder[i] - inorder[i - 1] < ans)
                ans = inorder[i] - inorder[i - 1];
        }
        return ans;
    }
    void inorderRec(TreeNode *node){//inorder遞迴
        if(!node) return;
        inorderRec(node->left);
        inorder.push_back(node->val);
        inorderRec(node->right);
        return;
    }
private:
    vector<int> inorder;
};

## 程式碼 (without inorder list)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDiffInBST(TreeNode* root) {
        diff = INT_MAX;
        prev = NULL;
        inorderRec(root);
        return diff;
    }
private:
    void inorderRec(TreeNode *node){
        if(!node) return;
        inorderRec(node->left);
        if(prev)//prev != NULL
            diff = min(diff, node->val - prev->val);//更新最小值
        prev = node;//記錄好前一個
        inorderRec(node->right);
        return;
    }
    TreeNode *prev;//存前一個
    int diff;
};