Find Mode in Binary Search Tree

最新推荐文章于 2024-04-09 22:21:57 发布

小灰灰52309

最新推荐文章于 2024-04-09 22:21:57 发布

阅读量203

点赞数

CC 4.0 BY-SA版权

分类专栏： leetcode ACM 文章标签： Find Mode in Binary

本文链接：https://blog.youkuaiyun.com/xiaohuihui52309/article/details/70858622

leetcode 同时被 2 个专栏收录

185 篇文章

订阅专栏

ACM

127 篇文章

订阅专栏

本文介绍了一种算法，该算法通过一次中序遍历来找出二叉搜索树中的众数（即出现频率最高的元素）。文章详细解释了如何统计元素出现的频率，并最终找出众数。

Find Mode in Binary Search Tree

Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST.

Assume a BST is defined as follows:

The left subtree of a node contains only nodes with keys less than or equal to the node's key.
The right subtree of a node contains only nodes with keys greater than or equal to the node's key.
Both the left and right subtrees must also be binary search trees.

For example:
Given BST [1,null,2,2],

return [2].

Note: If a tree has more than one mode, you can return them in any order.

解析：

二叉搜索树中序遍历的序列是递增排序数列，先遍历一遍统计其中出现次数最高的频率，然后再把出现频率最高的那些数找出来。

代码：

/**
 * 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> findMode(TreeNode* root) {
        vector<int> ans;
        int cnt=0;
        int curcount=0;
        int maxcoutn=0;
        int cur=INT_MIN;
        Mode(root,ans,0,curcount,maxcoutn,cur);
        curcount=0;
        cur=INT_MIN;
         Mode(root,ans,1,curcount,maxcoutn,cur);
         return ans;
    }
    void Mode(TreeNode* root,vector<int>&mode,int flag,int &curcount,int &maxcount,int &cur)
    {
        if (root==NULL)
        return ;
        Mode(root->left,mode,flag,curcount,maxcount,cur);
        if (cur==root->val)
        {
            curcount++;
        }
        else
        {
            curcount=1;
            cur=root->val;
        }
        
        if (curcount>maxcount)
        {
            maxcount=curcount;
        }
        else if(curcount==maxcount)
        {
            if (flag==1)
            {
                mode.push_back(cur);
            }
        }
        
        Mode(root->right,mode,flag,curcount,maxcount,cur);
        return ;
        
    }
    
};