image.png

思路就是二叉树的中序遍历
对于一个二叉搜索树来说，它的中序遍历会是一个排序数组
排序后相同的数都会出现在某一段

class Solution {
public:
    int maxSize = 0;
    vector<int> findMode(TreeNode* root) {
    vector<int> res;
    int base = NULL;
    int count = NULL;
    findModeHelp(root, base, count, res);
    return res;
    }

void findModeHelp(TreeNode* root, int & base, int & count, vector<int> & res){
    if(root == NULL) return;
    
    
    
    findModeHelp(root->left, base, count, res);
    
    if(base == NULL && count == NULL){
        // cout<<"middle trace initialize: "<<root->val<<endl;
        base = root->val;
        count = 1;
        maxSize = count;
        res.push_back(base);
    }
    else{
        // cout<<"middle trace: "<<root->val<<endl;
        // cout<<"base: "<<base<<endl;
        // cout<<"count: "<<count<<endl;
        // cout<<"maxSize: "<<maxSize<<endl;
        if(root->val == base) {
            count++;
            if(count > maxSize){
                res.clear();
                res.push_back(base);
                maxSize = count;
            }
            else if(count == maxSize){
                res.push_back(base);
            }
        }
        else{ // 前一数值结束
            base = root->val;
            count = 1;
            if(count == maxSize) res.push_back(base);
        }
        
    }
    
    findModeHelp(root->right, base, count, res);
}
};