Leetcode 501: mode in binary search tree

The mode in the binary search tree

subject ：

Ideas ：

Use pre Nodes and root Nodes
use count To record the number of times the node value is repeated
① Make sure the count Value to determine whether to add root value
if pre by null, perhaps pre and root When the values are not equal Start counting ; If pre and root Equivalent rule count++ Add up
② use count and max Compare , If count Than max Big , Then before list None of them are valid , eliminate list
if count=max, That is, a new mode appears , Added to the list
if count<max, Ignore

class Solution {
    
    int count=0;
    int max=Integer.MIN_VALUE;
    TreeNode pre=null;
    ArrayList<Integer> list;
    public int[] findMode(TreeNode root) {
    
        list=new ArrayList<>();
        check(root);
        int n=list.size();
        int[]r =new int[n];
        for(int i=0;i<n;i++){
    
            r[i]=list.get(i);
        }
        return r;

    }

    void check(TreeNode root){
    
        if(root==null){
    
            return;
        }
        check(root.left);
        // In the sequence traversal 
        // Start counting , Recount 
        if(pre==null || pre.val!=root.val){
    
            count=1;
        }else if(root.val==pre.val){
    
            count++;
        }

    // Deposit results 
        if(count>max){
      //  If there are duplicates, only count The value of the highest node ！
            list.clear();
            list.add(root.val);
            max=count;
        }else if(count==max){
    
            list.add(root.val);
        }
        //count<max Then it doesn't exist 
        pre=root;
        check(root.right);
    }


}