Minimum Absolute Difference in BST && Find Mode in Binary Search Tree

Minimum Absolute Difference in BST的思路就是BST中序遍歷，得到的就是從小到大排的順序，然後依次算兩個的差，就能得到最小值

/**
 * 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 minre = INT_MAX;
    TreeNode *prev=NULL;
    int getMinimumDifference(TreeNode* root) {
        if(root==NULL)
        return minre;
        getMinimumDifference(root->left);
        if(prev!=NULL)
        {
            minre=min(minre,root->val-prev->val);
        }
        prev=root;
        getMinimumDifference(root->right);
        return minre;
    }
   
};

Find Mode in Binary Search Tree的道理也是一樣的，還是中序遍歷，然後算每個數出現了幾次，找到出現次數最多的（用一個Count和CurrentCount，一個計算目前出現過的最大次數，另一個算當前數字出現的次數，兩個比）

/**
 * 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:
    vector<int> re;
    int count=1;
    int currentCount=1;
    TreeNode *prev=NULL;
    vector<int> findMode(TreeNode* root) {
        if(root==NULL)
        return re;
        
        findMode(root->left);
        if(prev!=NULL)
        {
            if(root->val==prev->val)
            {
                currentCount++;
                if(currentCount==count)
                {
                    re.push_back(prev->val);
                }
                else if(currentCount>count)
                {
                    re.clear();
                    re.push_back(prev->val);
                    count=currentCount;
                }
            }
            else
            {
                currentCount=1;
                
            }
        }
        prev=root;
        if(count==1)
            {
            re.push_back(root->val);
            }
        findMode(root->right);
        return re;
        
    }
};