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],
1
\
2
/
2
return [2].
Note: If a tree has more than one mode, you can return them in any order.
Follow up: Could you do that without using any extra space? (Assume that the implicit stack space incurred due to recursion does not count).
/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
int? prev = null;
int count = 1;
int max = 0;
public int[] FindMode(TreeNode root) {
var list = new List<int>();
InOrder(root,list);
return list.ToArray();
}
private void InOrder(TreeNode root, List<int> list){
if(root==null){
return;
}
InOrder(root.left, list);
if(prev != null){
if(root.val==prev){
count++;
}
else{
count = 1;
}
}
if(count>max){
max = count;
list.Clear();
list.Add(root.val);
}
else if(count == max){
list.Add(root.val);
}
prev = root.val;
InOrder(root.right, list);
}
}
Time Complexity: O(n)
Space Complexity: O(n) // for recursion stack.